Squid make sure to set “email_err_data off”

[JonathanLee]

Just learned about this bug there is a patch and there is a work around.

This was sent out from Amos Jeffries on the Squid email system. If you are not part of it here it is.

Credits:
This vulnerability was discovered by Leonardo Giovannini of
Doyensec.

Fixed by Amos Jeffries of Treehouse Networks Ltd.

Squid Proxy Cache Security Update Advisory SQUID-2025:2

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Advisory ID: | SQUID-2025:2
Date: | Oct 15, 2025
Summary: | Information Disclosure in Error handling.
Affected versions: | Squid 3.x -> 3.5.28
| Squid 4.x -> 4.17
| Squid 5.x -> 5.9
| Squid 6.x -> 6.14
| Squid 7.x -> 7.1
Fixed in version: | Squid 7.2

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Problem Description:

Due to a failure to redact HTTP Authentication credentials
Squid is vulnerable to an Information Disclosure attack.

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Severity:

This problem allows a script to bypass Browser security
protections and learn the credentials a trusted client uses to
authenticate.

This problem potentially allows a remote client to identify
security tokens or credentials used internally by a web
application using Squid for backend load balancing.

These attacks do not require Squid to be configured with HTTP
Authentication.

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Updated Packages:

This bug is fixed by Squid version 7.2.

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/0951a0681011dfca3d78c84fd7f1e19c78a4443f

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:

The following test can be used to determine if your Squid has
a vulnerable configuration:

squid -k parse 2>&1 | grep "email_err_data"

All Squid with email_err_data off are not vulnerable.

All Squid up to and including 7.1 with email_err_data on
are vulnerable.

All Squid up to and including 7.1 without email_err_data
are vulnerable.

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Workaround:

Disable debug information in administrator mailto links
generated by Squid. By configuring squid.conf with:

email_err_data off

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Contact details for the Squid project:

[JonathanLee]

Set this inside of custom options like

Example:

(ignore ssl_engine)

After run Squid -k parse and you should see this within the tests if you have no errors and it moves to the next time you have the work around.

2025/10/17 07:02:07| Processing: ssl_engine devcrypto
2025/10/17 07:02:07| Processing: email_err_data off