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Certificate SAN ip addresses not checked correctly for GSKit TLS provider #3102

matthew1001 opened this issue Oct 5, 2018 · 2 comments


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I did this

Ran an HTTPS application using libcurl + GSKit TLS provider, connecting to a server at who's certificate contains a SAN of:

IP Address:
DNS Name: localhost
IP Address:
DNS Name: my.local.server

I expected the following

For the connection to succeed

curl/libcurl version

curl 7.61.0 (x86_64-pc-linux-gnu) libcurl/7.61.0
Release-Date: 2018-07-11
Protocols: dict file ftp ftps gopher http https imap imaps pop3 pop3s rtsp smtp smtps telnet tftp
Features: AsynchDNS IPv6 Largefile SSL UnixSockets

operating system

Fedora 28


It appears that the implementation of Curl_verifyhost in x509asn1.c does a memcmp of &addr and q (where q = Curl_getASN1Element(...)). Running with a debugger appears to show that (name.end - q) = 0, which when compared to addrlen fails, preventing the memcmp even happening.

I wonder if it should it be comparing addrlen to (name.end - name.beg) & memcmp-ing &addr with name.beg?

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jay commented Oct 5, 2018

Yeah that doesn't look right. On success the pointer assigned to q should always be the same as what was assigned to name.end which means it would always be 0. I almost can't believe nobody's ever caught that though it must not be a heavily used function since it's gskit. I agree your solution sounds correct. Are you able to test it out and write up a PR for it?

@bagder bagder added the TLS label Oct 5, 2018
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I believe my local patch is working correctly. I'll look at submitting a PR.

matthew1001 added a commit to matthew1001/curl that referenced this issue Oct 15, 2018
field of a certificate.

For IP addresses in the subject alternative name field, the length
of the IP address (and hence the number of bytes to perform a
memcmp on) is incorrectly calculated to be zero. The code previously
subtracted q from name.end. where in a successful case q = name.end
and therefore addrlen equalled 0. The change modifies the code to
subtract name.beg from name.end to calculate the length correctly.

Fixes curl#3102
@jay jay closed this as completed in df54b14 Oct 16, 2018
@lock lock bot locked as resolved and limited conversation to collaborators Jan 14, 2019
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3 participants