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Squid Proxy Cache Security Update Advisory SQUID-2026:4
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Advisory ID: | SQUID-2026:4 (CVE-2026-47729)
Date: | 2026-06-14
Summary: | Memory disclosure in FTP gateway
Affected versions: | Squid 3.x -> 3.5.27
| Squid 4.x -> 4.17
| Squid 5.x -> 5.9
| Squid 6.x -> 6.14
| Squid 7.x -> 7.5
Fixed in version: | 7.6
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Problem Description:
Due to a Improper Validation of Syntactic Correctness of Input
bug, Squid is vulnerable to a Out-of-bounds Read
attack against the FTP gateway.
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Severity:
This problem allows a trusted client to perform an Out-of-Bounds
Read from random unrelated transactions when accessing a
misbehaving FTP server through Squid's gateway feature.
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Updated Packages:
This bug is fixed by Squid version 7.6
In addition, patches addressing this problem for the stable
releases can be found in our patch archives:
Squid 7:
<https://github.com/squid-cache/squid/commit/865a131c7d557e68c965043d98c2eccae26deef8.patch>
If you are using a prepackaged version of Squid then please
refer to the package vendor for availability information on
updated packages.
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Determining if your version is vulnerable:
Squid older than 3.5.28 have not been tested and should be
assumed to be vulnerable.
All Squid-4.x are vulnerable.
All Squid-5.x are vulnerable.
All Squid-6.x are vulnerable.
All Squid-7.x up to and including 7.5 are vulnerable.
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Workaround:
Place these squid.conf settings above any custom
'http_access allow' lines in your squid.conf:
acl FTP proto FTP
acl ftp_allowlist url_regex ^ftp://trusted\.server\.example\.com
http_access deny FTP !ftp_allowlist
Note: The ftp_allowlist ACL is optional, for those who need to
allow some FTP access to trusted servers. Best workaround
is not to use one unless necessary.
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Contact details for the Squid project:
For installation / upgrade support on binary packaged versions
of Squid: Your first point of contact should be your binary
package vendor.
If you install and build Squid from the original Squid sources
then the <[email protected]> mailing list is
your primary support point. For subscription details see
<https://www.squid-cache.org/Support/mailing-lists.html>.
For reporting of non-security bugs in the latest STABLE release
the squid bugzilla database should be used
<https://bugs.squid-cache.org/>.
For reporting of security sensitive bugs send an email to the
<[email protected]> mailing list. It's a closed
list (though anyone can post) and security related bug reports
are treated in confidence until the impact has been established.
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Credits:
This vulnerability was discovered and reported independently by
Pavel Kohout of Aisle Research, and
Lam Jun Rong of Calif.io in collaboration with Anthropic Research, and
Youssef Awad of CTF.ae
Fixed by Alex Rousskov, The Measurement Factory.
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Revision history:
2026-03-04 12:41:54 UTC Initial Report by Pavel Kohout of Aisle Research
2026-04-17: Initial Report by Lam Jun Rong
2026-05-07: Initial Report by Youssef Awad
2026-05-17 06:04:47 UTC patch published
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END
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