[squid-announce] [ADVISORY] SQUID-2020:9 Denial of Service processing Cache Digest Response

[Amos Jeffries]

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Squid Proxy Cache Security Update Advisory SQUID-2020:9
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Advisory ID:       | SQUID-2020:9
Date:              | August 23, 2020
Summary:           | Denial of Service
                   | processing Cache Digest Response
Affected versions: | Squid 3.x -> 3.5.28
                   | Squid 4.x -> 4.12
                   | Squid 5.x -> 5.0.3
Fixed in version:  | Squid 4.13 and 5.0.4
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    CVE Assignment pending
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Problem Description:

 Due to Improper Input Validation Squid is vulnerable to a Denial
 of Service attack against the machine operating Squid.

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Severity:

 This problem allows a trusted peer to deliver to perform Denial
 of Service by consuming all available CPU cycles on the machine
 running Squid when handling a crafted Cache Digest response
 message.

 This attack is limited to Squid using cache_peer with cache
 digests feature.

CVSS Score of 9.5
<https://nvd.nist.gov/vuln-metrics/cvss/v3-calculator?vector=AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H/E:H/RL:O/RC:C/CR:X/IR:X/AR:H/MAV:N/MAC:L/MPR:X/MUI:N/MS:C/MC:N/MI:N/MA:H&version=3.1>

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Updated Packages:

This bug is fixed by Squid versions 4.13 and 5.0.4.

 In addition, patches addressing this problem for the stable
 releases can be found in our patch archives:

Squid 4:
 <http://www.squid-cache.org/Versions/v4/changesets/SQUID-2020_9.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:

 All Squid built using --disable-cache-digests are not vulnerable.

 All Squid without cache_peer directives configured are not
 vulnerable.

 All Squid-3.x up to and including 3.5.28 using cache_peer
 directives with no-digest option configured are not vulnerable.

 All Squid-3.x up to and including 3.5.28 using cache_peer
 directives without the no-digest option configured are
 vulnerable.

 All Squid-4.x up to and including 4.12 using cache_peer
 directives with no-digest option configured are not vulnerable.

 All Squid-4.x up to and including 4.12 using cache_peer
 directives without the no-digest option configured are
 vulnerable.

 All Squid-5.x up to and including 5.0.3 using cache_peer
 directives with no-digest option configured are not vulnerable.

 All Squid-5.x up to and including 5.0.3 using cache_peer
 directives without the no-digest option configured are
 vulnerable.

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Workaround:

Either,

 Add the no-digest option to all cache_peer lines in squid.conf

Or,

 Build Squid with --disable-cache-digests

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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 <squid-users at lists.squid-cache.org> mailing list is your
 primary support point. For subscription details see
 <http://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
 <http://bugs.squid-cache.org/>.

 For reporting of security sensitive bugs send an email to the
 <squid-bugs at lists.squid-cache.org> 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 by Lubos Uhliarik of RedHat.

 Fixed by Eduard Bagdasaryan (The Measurement Factory).

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Revision history:

 2019-09-30 17:12:18 UTC Initial Report
 2020-07-29 20:51:58 UTC Fix committed
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