CivetWeb WebSocket Frame read_websocket buffer overflow

Summaryinfo

A vulnerability was found in CivetWeb. It has been classified as very critical. The affected element is the function read_websocket of the component WebSocket Frame Handler. This manipulation causes buffer overflow. This vulnerability appears as CVE-2026-29035. The attack may be initiated remotely. There is no available exploit.

Detailsinfo

A vulnerability classified as very critical was found in CivetWeb (unknown version). Affected by this vulnerability is the function read_websocket of the component WebSocket Frame Handler. The manipulation with an unknown input leads to a buffer overflow vulnerability. The CWE definition for the vulnerability is CWE-120. The product copies an input buffer to an output buffer without verifying that the size of the input buffer is less than the size of the output buffer, leading to a buffer overflow. As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

CivetWeb (commit 4a4f0c95) contains a heap and stack buffer overflow vulnerability in the read_websocket() function that allows unauthenticated remote attackers to corrupt memory by sending compressed WebSocket frames when both USE_ZLIB and MG_EXPERIMENTAL_INTERFACES are defined. Attackers can negotiate permessage-deflate during the WebSocket handshake and send a crafted frame with the RSV1 bit set, causing the server to write a 4-byte zlib sync trailer out-of-bounds past the allocated buffer, leading to heap metadata corruption, denial of service, or potential code execution.

It is possible to read the advisory at github.com. This vulnerability is known as CVE-2026-29035 since 03/03/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. Technical details of the vulnerability are known, but there is no available exploit. The pricing for an exploit might be around USD $0-$5k at the moment (estimation calculated on 08/11/2026).

Applying the patch 4a4f0c95 is able to eliminate this problem.

Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Productinfo

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• CivetWeb

CPE 2.3info

• 🔒

CPE 2.2info

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