CivetWeb up to 1.16 handle_http2 use after free

Summaryinfo

A vulnerability, which was classified as critical, has been found in CivetWeb up to 1.16. The affected element is the function handle_http2. This manipulation causes use after free. This vulnerability is tracked as CVE-2026-124040. The attack is possible to be carried out remotely. No exploit exists.

Detailsinfo

A vulnerability was found in CivetWeb up to 1.16. It has been declared as critical. Affected by this vulnerability is the function handle_http2. The manipulation with an unknown input leads to a use after free vulnerability. The CWE definition for the vulnerability is CWE-416. The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer. As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

CivetWeb through 1.16, when built with USE_HTTP2 and enable_http2 on, contains a use-after-free vulnerability in handle_http2() that retains freed :method and :path pointers. Unauthenticated remote attackers can send a later HEADERS frame omitting these pseudo-headers to influence request method or path seen by access rules, or crash the server.

The advisory is shared at github.com. This vulnerability is known as CVE-2026-124040 since 11/06/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. Technical details are known, but no exploit is available. The price for an exploit might be around USD $0-$5k at the moment (estimation calculated on 11/06/2026).

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

Name

• CivetWeb

Version

• 1.0
• 1.1
• 1.2
• 1.3
• 1.4
• 1.5
• 1.6
• 1.7
• 1.8
• 1.9
• 1.10
• 1.11
• 1.12
• 1.13
• 1.14
• 1.15
• 1.16

Website

• Product: https://github.com/civetweb/civetweb/

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Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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