CivetWeb Heap/Stack Buffer Overflow via WebSocket permessage-deflate Decompression (CVE-2026-29035) | HOL Guard CVE

Medium · CVSS 6.5CVE-2026-29035

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

Answer in brief

CVE-2026-29035 records a Medium severity (CVSS 6.5) vulnerability in CivetWeb Heap/Stack Buffer Overflow via WebSocket permessage-deflate Decompression. The current sources do not mark it as known exploited. The current feed maps civetweb/civetweb (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Aug 11, 2026Updated Aug 14, 2026Source checked Sep 25, 2026First seen by HOL Aug 11, 2026Material review Aug 14, 2026

Upstream Advisory

Key facts

Risk: Medium · CVSS 6.5
Exploitation: Not marked as known exploited
Affected software: 1 mapped package or product
Fix availability: Not reported

Why this deserves its current priority

CVSS is 6.5. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps civetweb/civetweb (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
civetweb/civetwebgeneric	0	Not reported

Recommended response

Check inventory. Check lockfiles and deployed manifests for civetweb/civetweb.
Review the reported fix. Monitor this advisory for an available fix and review any installs of the affected package.

Evidence timeline and material changes

Published upstream
Aug 11, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Aug 14, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Aug 11, 2026

Sources and claim methodology

Upstream source 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.

Quoted source text, attributed separately from HOL analysis.