v11.0.506

C-Kermit 11.0 announcement (11.0.506)

August 3, 2026

This is the public announcement of the release, and is a summary of all changes since the last full release, 9.0.302 in 2011.

Dedication

I dedicate this release of C-Kermit to Frank da Cruz.

Frank was directly involved with Kermit for 44 years, from its initial design in 1981 all the way through 2025. He maintained Kermit as an Open Source project after Columbia University ended its sponsorship. I know of no other Open Source project where the founder remains so personally involved for so long.

When Kermit was begun, transfers between different hardware and operating systems were difficult or impossible. Frank helped build a bridge. Kermit glued systems together, from the International Space Station to pocket calculators, and set a new standard for interoperability. It continues to do so.

Kermit is still one of the quietly-working pillars of computing today, enabling everything from firmware upgrades to radios. And, yes, it still reliably transfers files over serial lines.

As we start to spend a lot of time in the Kermit codebase, we do so standing on the shoulders of a giant. Thanks, Frank, for your decades of work on Kermit.

John Goerzen, July 2026

Summary

C-Kermit 11 is a major new release, the first non-beta since the last 9.x release in 2011. It represents a significant effort to modernize and improve the C-Kermit codebase.

Since all C-Kermit 10.x releases were betas, some people may be upgrading from 9.x and others from 10.x. Since some changes were labeled as "9.x DEV" or various alphas, but also never released, I indicate in which version a change was made with "9", "10", and "11" tags accordingly. Please see the history and FAQ pages for more information on the relationship between the different Kermit versions.

Major Architectural Improvements

• [11] Introduced C-based unit tests and a Python-based regression test suite. Together, these test suites have been responsible for identifying nearly all of the bug fixes in the v11 release as noted below. Timing analysis of the test suite also led to most of the performance fixes. Running the tests under load led to the discovery and fix of numerous race conditions.

  • [11] Also introduced compatibility tests that test the current release against gkermit, E-Kermit (eksw), and the last C-Kermit full release prior to 11.0 (9.0.302 from 2011). This also led to a fix for a bug dating back to C-Kermit 9.0.304 of 2012.

• [11] Added CI. All changes now are validated on Linux, MacOS, FreeBSD, and NetBSD using the above test suites. Over 1700 test cases are being run.

• [11] Binaries for multiple platforms are automatically built from CI at release time.

• [10] Codebase-wide modernization to support ANSI C and function prototyping, satisfying strict requirements in newer compilers while retaining backward compatibility with pre-ANSI systems.

New Features

• [11] C-Kermit's TCP stack now supports IPv6, while degrading gracefully to IPv4 on hosts that don't have IPv6 connectivity, or whose system libraries don't support IPv6. For more, see the new IPv6 in C-Kermit document.

• [11] There's now a tool that will extract all the help text from C-Kermit and write a nice Markdown file that acts as an up-to-date command reference for your specific platform. A generated version of this can be found at HELP reference.

• [11] SET COMPATIBILITY 9 and SET COMPATIBILITY 10 to easily change settings to maximize compatibility with C-Kermit 9.0.302 and 10.0 Beta.12, respectively. This restores previous behavior, which weakens Kermit's security posture. These settings can also be applied at startup by invoking Kermit as kermit9 or kermit10.

• [9] Android platform support, including NDK builds and a vanity herald.

• [9] Locale support for dates, times, and error messages (with Spanish and German translations), controllable via the --nolocale command-line option and K_NOLOCALE environment variable.

• [9] A new CHANGE command to search and replace strings in files, using standard directory and touch file-selection switches.

• [9] A new FOPEN /STDIN command to allow Kermit scripts to read standard input from a pipe.

Major Improvements

• [11] External protocol (Zmodem and the like) support has seen significant performance increases in many cases, due to elimination of inefficiencies in the pty code that supports it.

• [11] Codebase-wide dead code elimination and general simplification. This removes code that was never used in any build on any platform, and makes code auditing and analysis easier. Despite many new features, the C-Kermit 11 codebase (excluding comments) is about 2600 lines smaller than the last 10.x beta!

• [11] Now compatible with OpenSSL 3.x and 4.x. The OpenSSL runtime version check was relaxed to allow minor version updates, and support was added for compiling with NO_OPENSSL_VERSION_CHECK to disable the compatibility check.

• [11] Static binaries are now supported on Linux, with both glibc and musl libc. Official musl static binaries for Linux on amd64 and arm64 are built for each release.

• [11] Added a number of new pieces of documentation.

• [10] Support for serial-port speeds up to 4,000,000 bps.

• [9] Modernized FTP/SSL and Telnet/SSL negotiations to default to TLS 1.0+ and disable SSLv3 by default (POODLE mitigation), adding the use-ssl-v3 bug option for fallback compatibility.

Major Bugfixes

• [11] Certain packet sizes on the boundary between small and extended packet sizes could lead to a transfer being hung on all platforms. Fixed the bug in commit d560c58 and added extensive tests around this scenario. Bug introduced in C-Kermit 10.0 Beta.05 of 2022.

• [11] Fixed a data corruption bug that occurred during packet size renegotiation due to improperly using strlen() to determine the size of binary data that may contain NULL bytes. (commit b58e033) This issue was only observed by running the test suite on NetBSD, but the code pattern indicates it could occur on any platform given the correct circumstances. The bug was introduced in C-Kermit 5A(188) in 1992 in commit a213649.

• [11] Numerous pty issues were remedied on MacOS; some had been going back decades. In particular, MacOS FIONREAD appears to be unreliable, and assuming it to be reliable led to some hard-to-track-down hangs.

• [11] C-Kermit now is fully able to process filenames with embedded spaces due to numerous bugfixes in commit b06df38. Among them:

  • You can now use GET to retrieve a file whose name has embedded spaces (previously you could only SEND such a file).

  • MGET had bugs around quoting that inadvertently would strip necessary quote characters.

  • The Kermit Protocol treats a space as a delimeter between filenames, unless it is enclosed in braces. The C-Kermit client accepts both double quotes and braces as quoting characters. The client now will properly quote all filenames containing spaces with braces when sent to the server, regardless of which scheme the user selected.

  • Several REMOTE commands were broken with filenames with embedded spaces or escaped delimiters.

  • Numerous bugs relating to escaping of embedded quote/brace characters as part of filenames were fixed.

  • GET and SEND used inconsistent quoting rules.

• [11] Recursive transfer fixed on MacOS in commit f60a87e. The bug appears to have been introduced in C-Kermit 10.0 Beta.01, commit 1755b85 in 2022.

• [11] Fixed filename collision (overwrite) detection on MacOS. Same origin as the recursive issue.

• [11] Fixed a packet size negotiation bug that manifest itself in talking to E-Kermit (eksw). The bug was introduced in C-Kermit 9.0.305 of 2021-11-16.

• [11] Make sure timeval usec is initialized. It was used uninitialized, leading to undefined behavior that could corrupt the modification date by many seconds or minutes. The relevant code was added in C-Kermit 8.0.200 (commit c88d9b8 in 2001), but usec may not have been widely used at the time.

• [11] Added new SET PROTOCOL STARTUP-STRING to allow easy inhibiting of all startup strings where necessary.

• [11] When transferring multiple files in text mode, the system would detect Unicode encoding on only the first, and blindly apply that assumption to all the rest. Commit 93ffe02.

• [11] Fixed a bug where raw TLS connections could hang waiting for Telnet negotiation in commit 0b9dc4f. The issue appears to date back to at least C-Kermit 8.0.211 of 2004.

• [11] Fixed a bug in ttopen where pipe connections did not execute the configured command.

• [11] Found and fixed numerous buffer overruns and memory leaks.

• [11] Tracked down a pseudoterminal failure on NetBSD. It turns out to be a kernel bug in which the kernel can sometimes return a value indicating more data was successfully written down the pty than actually was, causing loss of bytes of data. When in default mode, C-Kermit detects this and automatically shrinks its packet size to compensate! (This is what exposed the strlen() bug mentioned elsewhere.) When in streaming mode, this is fatal to the transfer, and was detected when I added streaming mode tests. The workaround is to run sysctl -w kern.tty.qsize=65536 or to set it in /etc/sysctl.conf; a comment in that file implies this issue is known already.

• [11] Several other pty issues were also remedied on NetBSD.

• [11] Fix IKSD server refusing all connections when built with SSL support but not configured with an SSL cert. This had been a long-standing C-Kermit bug. Fixed in commit 5160132. Appears to have been introduced in C-Kermit 8.0.200 in 2001 with the introduction of the SSL code at that time.

• [10] Fixed the TOUCH command, which had been nonfunctional.

• [9] Fixed a crash on 64-bit platforms (such as OpenBSD sparc64) during file transfers due to conflicting int/long declarations.

• [9] Fixed a crash in Open Watcom Windows builds caused by inconsistent extern declarations of the vmode variable.

• [9] Fixed S-Expression processor core dumps when given invalid operators.

• [9] Fixed the DIRECTORY /BRIEF command to correctly honor the /EXCEPT switch.

• [9] Fixed a bug in zchko() that caused FTP GET commands to segment fault on systems with NOUUCP defined.

• [9] Added CK_64BIT support, significantly increasing command, macro, variable, and packet buffer sizes on 64-bit architectures.

Security and Reliability Improvements

• [11] More durable privilege dropping (priv_chk)

• [11] Elimination of a number of unbounded writes to buffers

• [11] Disable auto transfer mode by default, which switched between text and binary transfer modes based on a heuristic. For full details, see commit cdd2e25 and the discussion at https://bugs.debian.org/1121901 . The heuristic for attempting to guess the type of files is now disabled to avoid data corruption, letting Kermit always follow the user's expressed transfer type wishes by default.

• [11] Fix CVE-2025-68920, insecure defaults that previously would let a malicious remote kermit server perform actions on your local workstation. Further discussion in commit 9ee170a and full details at http://bugs.debian.org/1123025 . See more details under changed behavior below for how to adjust this in the rare event you might need to.

• [11] Switch the default SET FILE COLLISION from BACKUP to REJECT. The previous default would let a malicious remote overwrite sensitive local files (eg, .bashrc) which could lead to a security issue.

• [11] Fixed a bug where the CLEAR APC command could bypass APC safety checks or cause the parser to hang.

• [11] Disabled MAIL and PRINT handling by default (dc67bdd), and hardened the handling of them to prevent shell injection attacks (23ec736).

• [11] Added new receive confirmation, which prompts for confirmation before receiving a file with a name that wasn't specifically requested locally. This is governed by a new SET RECEIVE CONFIRM option, which defaults to ON. This does not prompt when running headless (ie, server or iksd).

• [10] Changed the default value of SET VARIABLE-EVALUATION to SIMPLE (non-recursive) to avoid evaluation issues with backslashes in pathnames on Windows and OS/2.

• [9] Fixed a bug where TOUCH /MODTIME could destroy existing files under certain conditions.

See the section below on changed behavior for highlights on the impact of changed defaults. This impact is expected to be rare.

Additional improvements and bugfixes

• [11] Fixed an unhandled exception warning on NetBSD

• [11] Prevent Kermit from killing all of the user's processes in certain edge cases where it may try to kill PID -1. Fixed in commit 72fa00b. Bug introduced in C-Kermit 9.0.302 of 2011.

• [11] Correct use of ziperm vs. ziperms for non-CK_PERMS platforms. Fixed in commit 3fcd731. Appears to have been latent since C-Kermit 7.0 in 2000.

• [11] Updated the list of text and binary extensions to have more modern filetypes, and fixed typos in the old list.

• [11] Improve transfer error reporting. Previously, errors might be reported on the transfer screen, then immediately wiped when switching back to the regular screen. Now report them on the regular screen also. A comment from 2001 suggested that after this work was done, a failed autodownload could drop the user back into CONNECT mode just like a successful one did. So, changed the default for SET TERMINAL AUTODOWNLOAD ERROR from STOP to CONTINUE.

• [11] Added new SET FILE SYSTEM-ID setting, which facilitates using C-Kermit to translate files between different platform conventions even when used on a single platform. It also facilitates testing these functions.

• [11] Allow pseudoterminals to work even when Kermit itself is not called from a controlling terminal.

• [11] Fixed Unicode text detection for very small files in commit dfd875f. Issue dates back to the introduction of this code in C-Kermit 9.0.302 in 2011.

• [11] Several improvements to help text

• [11] Fixed japanese-roman character set

• [10, 11] OS/2 compatibility improvements

• [11] Fixed command prompt formatting in anonymous IKSD when the home directory is root (/).

• [11] Fixed Gentoo builds after the ncurses tinfo library split.

• [11] Fixed SET HOST to work properly after an ssh command had been issued earlier in the same session. (10eb192) Bug introduced in C-Kermit 9.0.302 of 2011.

• [11] Fixed several issues where EINTR from read() could cause C-Kermit to improperly close a connection. In one case, signals such as SIGWINCH at particular times triggered this issue on Linux; in another, the test suite caused it on NetBSD.

• [11] Coincidentally, fixed a bug in winchh(), which is the handler for SIGWINCH, in which is fails to restore errno before returning, so an error from a call it makes can lead the interrupted code to believe an error other than EINTR occurred.

• [11] Fixed a bug in SSL network read that was triggered by ZModem over SSL, which resulted in exceptionally slow performance in certain circumstances

• [11] Fixed an issue with the telnet protocol handling of a NULL after a bare CR

• [11] Fixed build issues on OpenBSD

• [11] Fixed a bug on OpenBSD that could cause ZModem transfers to be truncated under heavy load

• [11] Now give an accurate error message instead of "write access to UUCP lockfile" about errors that had nothing to do with the lockfile

• [11] Fixing recursive receive, which led to a deep dive into C-Kermit permissions. See the new C-Kermit permissions documentation.

• [11] Added a workaround to the client to deal with old broken IKSD servers.

• [11] Fixed a telnet negotiation race related to EINTR and select

• [11] Fixed Unicode BOM detection issue that may manifest on big-endian architectures. Fixed in commit da4699c. Dates back to at least C-Kermit 8.0.200 of 2001, and possibly further.

• [11] Fixed backspace after typing the space in "ssh "

• [11] Fix macOS linker working, thanks to jj1bdx.

• [11] Added help text for HELP SHOW, describing each sub-option.

• [11] Properly define CK_WREFRESH on Linux and macOS. The original definition dates to C-Kermit 5A(190) in 1994 and appears to have just never been updated for these platforms.

• [10] Kermit scripts can now run as Unix pipelines

• [10] Added the VDIRECTORY command (with V as a one-letter synonym) as a shortcut for the DIRECTORY command.

• [10] Added new commands: GREP /DISPLAY, GREP /VERBATIM, GREP /MACRO, and GREP /ARRAY.

• [10] Added the ckubuildlog utility script to automate creating build report entries.

• [10] Added REMOTE CDUP and REMOTE STATUS server commands for conformity with DECSYSTEM-20 Kermit.

• [10] Fixed the DIRECTORY command to correctly handle multiple file specifications.

• [10] Fixed macOS COPY /APPEND to work correctly in ckubuildlog.

• [9] Fixed date parsing to correctly process leap years (e.g. 29-Feb) when calculating relative dates.

• [9] Fixed a memory leak in the CHANGE command where a dynamic buffer was not freed on repeated use.

• [9] Fixed local array persistence in macros where arrays declared local persisted after macro return.

• [9] Added substring filtering to the SHOW FUNCTIONS command (e.g. SHOW FUNCTION pid).

• [9] Reworked Linux makefile target to query ld for library paths dynamically rather than using hardcoded system paths.

Summary of new and changed commands and scripting functions

• [11] SET COMPATIBILITY

• [11] SET TCP ADDRESS-FAMILY (see IPv6 documentation)

• [11] SET TCP ADDRESS6 (see IPv6 documentation)

• [11] SET FILE SYSTEM-ID

• [11] SET PROTOCOL STARTUP-STRING

• [11] SET RECEIVE CONFIRM

• [10] VDIRECTORY (synonym V)

• [10] SET VARIABLE-EVALUATION

• [10] REMOTE CDUP and REMOTE STATUS

• [10] GREP switches /DISPLAY, /VERBATIM, /MACRO, and /ARRAY

• [9] CHANGE

• [9] TOUCH /MODTIME, /LIST, and /SIMULATE

• [9] FOPEN /STDIN

• [9] SET EXIT MESSAGE and SHOW EXIT

• [9] SET TEMP-DIRECTORY and SHOW TEMP-DIRECTORY

• [9] Added the \ffilecompare() function to compare file contents.

• [9] Added the \fdayname() and \fmonthname() functions for locale-aware day and month names.

• [9] Added the \fpictureinfo() function to extract camera and scanner Exif metadata (width, height, and date taken).

• [9] Added the \fnfileinfo() function to populate an array with file metadata.

• [9] Added the IF BINARY, IF TEXT, and IF FUNCTION conditional tests.

Summary of changed behavior

All items highlighted here are expected to rarely if ever cause an issue in the wild.

Invoking Kermit as kermit9 or kermit10 (copy or symlink kermit or wermit to those names) or using SET COMPATIBILITY will revert these changed settings to Kermit 9.0.302 or 10.0 Beta.12 settings as appropriate, restoring most of the old behavior (which weakens Kermit's security protections).

• [11] The default SET FILE COLLISION has changed from BACKUP to REJECT for security reasons. See the options for COLLISION under HELP SET FILE for more details. This is the one most likely to be user-visible.

• [11] On systems supporting IPv6, the same approach as telnet(1) on Linux will be used: if name resolution returns IPv6 and IPv4 addresses, the IPv6 address will be tried first if the system is configured with IPv6 addresses. If the IPv6 address fails to connect, the IPv4 address will be tried next. The previous behavior, which was always IPv4, can be restored with SET TCP ADDRESS-FAMILY IPV4.

• [11] Previous C-Kermit already used SET FILE TYPE BINARY, but unfortunately they had transfer-mode set to automatic, which would override the binary file type in surprising circumstances, leading to data loss. The default is now SET TRANSFER-MODE MANUAL. Previous behavior can be restored by using SET TRANSFER-MODE AUTOMATIC. See discussion above under security and at https://bugs.debian.org/1121901 .

• [11] You may still set transfer-mode to be automatic. If you do, the sets of extensions used to help determine text or binary files have been revised with modern filetypes, and had typos corrected. (976a974)

• [11] When C-Kermit is used as a client, it may connect to an untrusted remote system (for instance, a BBS). By default, the remote Kermit was able to make changes to, and retrieve data from, the local system. This scenario would be been used exceptionally rarely for legitimate purposes. You can type enable ? to see the list of commands you can re-enable. See the discussion above under CVE-2025-68920. (9ee170a and dc67bdd)

• [11] Since C-Kermit now properly reports errors during autodownload, the default for SET TERMINAL AUTODOWNLOAD ERROR has changed from STOP to CONTINUE as suggested by a comment in 2001.

• [11] A minor change to the handling of paths in received files, allowing /RECURSIVE to work for received files by default again (with more path safeguards). For more details, see the permissions documentation. This mostly restores the pre-11.0 behavior for recursive receives, but with added safeguards.

• [11] Added new receive confirmation, which prompts for confirmation before receiving a file with a name that wasn't specifically requested locally. This is governed by a new SET RECEIVE CONFIRM option, which defaults to ON. This does not prompt when running headless (ie, server or iksd). It will generally not trigger on things requested via GET since the user is known to have requested a file. SET RECEIVE CONFIRM OFF will restore previous behavior.

• [11] The bugfixes for filenames with embedded spaces or quoting characters/braces in commit b06df38 may cause requests that previously failed to now succeed.

• [10] The default SET VARIABLE-EVALUATION setting has changed from RECURSIVE to SIMPLE to prevent pathnames containing backslashes from being incorrectly evaluated recursively.

• [10] wtmp and syslog logging are no longer enabled by default and must be explicitly enabled at compile time.

• [10] The \v(version) variable and --version command-line parameters no longer show major.minor.edit, just major.minor. The edit number is still part of the startup herald and the VERSION command's banner, and of \v(fullversion).

• [9] The MOVE command was changed to be a synonym for RENAME by default (previous behavior can be restored with compile-time -DOLDMOVE).

• [9] Default command prompt on Unix now collapses the home directory path prefix to ~/.

• [9] The SET TELNET WAIT setting is no longer silently overridden to ON by Telnet option negotiations.

• [9] Removed the undocumented ok keyword as an alias for SUCCESS in IF statements.

C-Kermit 11.0.506 updates since 11.0.505

• Skip FTP tests when Kermit is built with -DNOFTP, as the Gentoo package does.

• Address macOS linker warning. Patch from jj1bdx.

• Added help text for HELP SHOW, describing each sub-option.

• Properly define CK_WREFRESH on Linux and macOS. The original definition dates to C-Kermit 5A(190) in 1994 and appears to have just never been updated for these platforms.

• [security] Added new receive confirmation, which prompts for confirmation before receiving a file with a name that wasn't specifically requested locally. This is governed by a new SET RECEIVE CONFIRM option, which defaults to ON. This does not prompt when running headless (ie, server or iksd).

• C-Kermit now is fully able to process filenames with embedded spaces due to numerous bugfixes in commit b06df38. Among them:

  • You can now use GET to retrieve a file whose name has embedded spaces (previously you could only SEND such a file).

  • MGET had bugs around quoting that inadvertently would strip necessary quote characters.

  • The Kermit Protocol treats a space as a delimeter between filenames, unless it is enclosed in braces. The C-Kermit client accepts both double quotes and braces as quoting characters. The client now will properly quote all filenames containing spaces with braces when sent to the server, regardless of which scheme the user selected.

  • Several REMOTE commands were broken with filenames with embedded spaces or escaped delimiters.

  • Numerous bugs relating to escaping of embedded quote/brace characters as part of filenames were fixed.

  • GET and SEND used inconsistent quoting rules.

• Added new document about filenames with spaces, wildcards, and escaping

• Introduced compatibility tests that test the current release against gkermit, E-Kermit (eksw), and the last C-Kermit full release prior to 11.0 (9.0.302 from 2011).

• Fixed a packet size negotiation bug that manifest itself in talking to E-Kermit (eksw). The bug was introduced in C-Kermit 9.0.305 of 2021-11-16.

• SET COMPATIBILITY 9 and SET COMPATIBILITY 10 to easily change settings to maximize compatibility with C-Kermit 9.0.302 and 10.0 Beta.12, respectively. This restores previous behavior, which weakens Kermit's security posture. These settings can also be applied at startup by invoking Kermit as kermit9 or kermit10.