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Vulnerabilities CVE-2026-29035

CVE-2026-29035

High
Open
TLP:CLEAR

CivetWeb Heap/Stack Buffer Overflow via WebSocket permessage-deflate Decompression

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Description

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.

Details

CVSS Score
8.3
EPSS Score
0.47%

38.2th percentile

CVSS Vector
CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:L/VA:H/SC:N/SI:N/SA:N
Confidence
90%
Published
Aug 11, 2026
Last Modified
Aug 12, 2026
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