High [CVE-2026-29035] Arbitrary code execution via crafted WebSocket frames
This high-severity Red Hat Linux advisory covers CVE-2026-29035.
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Summary
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. A flaw was found in CivetWeb.
This could lead to memory corruption, potentially resulting in denial of service or arbitrary code execution. The vulnerability occurs during the `permessage-deflate` decompression process when specific experimental interfaces are enabled.
Exploitation requires the `USE_ZLIB` and `MG_EXPERIMENTAL_INTERFACES` features to be enabled, which are not default configurations in Red Hat products. Red Hat severity: Important — CVSS 7.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).
Weakness: CWE-787.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative — check it before change work.
Official advisory · high-confidence parse· fetched 3 hours ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists — confirm against the vendor advisory.
Official advisory · high-confidence parse· fetched 3 hours ago·verify at source
Mitigation checklist
- To mitigate this vulnerability, ensure that CivetWeb is compiled without the `USE_ZLIB` and `MG_EXPERIMENTAL_INTERFACES` flags enabled. If CivetWeb is deployed as a library, applications linking against it should avoid enabling these experimental WebSocket features. Disabling these features prevents the vulnerable code path from being active.
Official advisory · high-confidence parse· fetched 3 hours ago·verify at source
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