CVE-2025-49812: Apache HTTP Server: mod_ssl TLS upgrade attack

Severity: high (CVSS 7.4 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.6% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-07-10 · updated 2026-06-17
Weakness: CWE-287

Description

In some mod_ssl configurations on Apache HTTP Server versions through to 2.4.63, an HTTP desynchronisation attack allows a man-in-the-middle attacker to hijack an HTTP session via a TLS upgrade. Only configurations using "SSLEngine optional" to enable TLS upgrades are affected. Users are recommended to upgrade to version 2.4.64, which removes support for TLS upgrade.

Affected products

Apache HTTP Server: before 2.4.64 — fixed in 2.4.64

How to fix

Upgrade to a fixed version: Apache HTTP Server 2.4.64. Check the vendor advisory for mitigations.

References

https://httpd.apache.org/security/vulnerabilities_24.html
http://www.openwall.com/lists/oss-security/2025/07/09/3
http://www.openwall.com/lists/oss-security/2025/07/10/2
http://www.openwall.com/lists/oss-security/2025/07/10/9
https://lists.debian.org/debian-lts-announce/2025/08/msg00009.html

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