Fix heap-buffer-overflow in TelnetLayer due to stale offset in getOption/getOptionData (#2144)#2148
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seladb merged 4 commits intoMay 26, 2026
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In getOption(TelnetCommand) and getOptionData(TelnetCommand, size_t&), the 'offset' variable was calculated before getNextCommandField() advanced 'pos', causing a stale value to be used as maxLength in subsequent getFieldLen() calls. This allowed distanceToNextIAC() to set an endIt pointer past the end of the allocated buffer, triggering an out-of-bounds read in std::find() inside findNextIAC(). Fix: recalculate offset from the updated pos after getNextCommandField(). Also fix getOptionData(TelnetCommand, size_t&) which incorrectly used m_Data instead of pos when extracting field data for the matched command. Fixes: seladb#2144
Test TelnetCommandAfterDataParsingTests verifies that getOption(TelnetCommand) and getOptionData(TelnetCommand, size_t&) work correctly when user data (escaped IAC) precedes a command field, which previously caused a heap-buffer-overflow due to stale offset calculation.
Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## dev #2148 +/- ##
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+ Coverage 82.66% 82.70% +0.04%
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Files 332 332
Lines 59736 59746 +10
Branches 12392 12332 -60
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+ Hits 49378 49412 +34
+ Misses 9480 8928 -552
- Partials 878 1406 +528
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seladb
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May 25, 2026
alacrity-aya
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May 26, 2026
- Reuse offset in TelnetLayer loops instead of introducing new variables - Rename regression test to TelentCommandInvalidDataTests - Use auto* for telnetLayer in test code - Add telnetCommandAfterData.pcap to PacketExamples for Wireshark inspection
- Reuse offset during Telnet command scans in TelnetLayer - Rename invalid-data regression test and keep registrations in sync - Use auto* in Telnet regression test code - Add telnetCommandAfterData.pcap fixture for easier packet inspection
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Contributor
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@seladb I don't know why ci failed. Can you take a look? |
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@alacrity-aya It happens sometimes due to the environment the CI runs on. |
seladb
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May 26, 2026
Owner
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Thank you @alacrity-aya for working on this fix! 🙏 |
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Summary
Fixes #2144
This PR fixes a heap-buffer-overflow in
TelnetLayerthat occurs whencalling getOption(TelnetCommand) or getOptionData(TelnetCommand, size_t&)
on a Telnet packet where user data (escaped IAC
FF FF) precedes a command field.Root Cause
In both getOption(TelnetCommand) and getOptionData(TelnetCommand, size_t&),
the
offsetvariable was calculated before getNextCommandField() advancedpos, and then used unmodified when computingmaxLengthfor the subsequentgetFieldLen() call: