CVE-2023-46724: SQUID-2023:4 Denial of Service in SSL Certificate validation

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 4.0% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2023-11-01 · updated 2026-06-17
Weakness: CWE-125

Description

Squid is a caching proxy for the Web. Due to an Improper Validation of Specified Index bug, Squid versions 3.3.0.1 through 5.9 and 6.0 prior to 6.4 compiled using `--with-openssl` are vulnerable to a Denial of Service attack against SSL Certificate validation. This problem allows a remote server to perform Denial of Service against Squid Proxy by initiating a TLS Handshake with a specially crafted SSL Certificate in a server certificate chain. This attack is limited to HTTPS and SSL-Bump. This bug is fixed in Squid version 6.4. In addition, patches addressing this problem for the stable releases can be found in Squid's patch archives. Those who you use a prepackaged version of Squid should refer to the package vendor for availability information on updated packages.

Affected products

Squid: from 3.3.0.1 before 6.4 — fixed in 6.4

How to fix

Upgrade to a fixed version: Squid 6.4. Check the vendor advisory for mitigations.

References

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