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libevent EUVDEUVD-2026-63562

| CVE-2026-63379 MEDIUM
HTTP Request/Response Smuggling (CWE-444)
2026-08-20 security-advisories@github.com
Request Smuggling Information Disclosure
6.3
CVSS 4.0 · Vendor: github
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Severity by source

Vendor (github) PRIMARY
6.3 MEDIUM
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
vuln.today AI
5.4 MEDIUM

AC:H reflects the required proxy infrastructure forwarding chunked trailers; S:C captures the proxy-to-backend trust boundary crossing enabling the smuggling.

3.1 AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:N
4.0 AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N
SUSE
6.5 MEDIUM
AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

Primary rating from Vendor (github).

CVSS VectorVendor: github

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
X

Lifecycle Timeline

3
Patch available
Aug 20, 2026 - 19:03 EUVD
Source Code Evidence Fetched
Aug 20, 2026 - 18:41 vuln.today
Analysis Generated
Aug 20, 2026 - 18:41 vuln.today

DescriptionCVE.org

Libevent is an event notification library. Prior to 2.1.13 and 2.2.2-alpha, libevent processes chunked HTTP trailers in http.c through evhttp_read_trailer and merges them into request headers. The fix introduces evhttp_parse_headers_impl_ and a temporary trailer header list. An unauthenticated remote attacker can place security-sensitive fields in trailers so that an upstream proxy and the libevent application interpret different effective headers, enabling header smuggling, authorization bypass, proxy-header spoofing, or cache poisoning. The fix parses trailers into a temporary header list and discards them instead of merging them into req->input_headers. This issue is fixed in versions 2.1.13 and 2.2.2-alpha.

AnalysisAI

HTTP chunked trailer smuggling in libevent before 2.1.13 and 2.2.2-alpha allows unauthenticated remote attackers to inject security-sensitive header fields - such as Authorization or X-Forwarded-For - via chunked transfer encoding trailers that libevent merges directly into its request header store. In deployments fronted by a reverse proxy, the proxy evaluates the original headers while libevent processes the attacker-supplied trailers as authoritative input headers, enabling authorization bypass, proxy-header spoofing, and cache poisoning. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

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Vulnerability AssessmentAI

Exploitation Exploitation requires an upstream reverse proxy (nginx, HAProxy, Varnish, Apache httpd in proxy mode, or similar) that forwards HTTP/1.1 chunked requests to a libevent-based backend without stripping or normalizing chunked trailers. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The CVSS 4.0 score of 6.3 with AT:P correctly represents that exploitation is conditioned on a specific deployment topology: an upstream reverse proxy must forward chunked HTTP/1.1 requests to a libevent-based backend without stripping trailers, and the application must perform security-relevant decisions based on header values. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario Full exploit scenario with step-by-step reproduction available after sign-in.
Remediation The primary fix is to upgrade libevent to 2.1.13-stable (2.1.x branch) or 2.2.2-alpha (2.2.x branch), available at https://github.com/libevent/libevent/releases/tag/release-2.1.13-stable and https://github.com/libevent/libevent/releases/tag/release-2.2.2-alpha. … Detailed patch versions, workarounds, and compensating controls in full report.
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Vendor StatusVendor

SUSE

Severity: Moderate
Product Status
SUSE Linux Enterprise Desktop 15 SP7 Affected
SUSE Linux Enterprise High Performance Computing 12 Affected
SUSE Linux Enterprise High Performance Computing 15 SP7 Affected
SUSE Linux Enterprise Micro 5.3 Affected
SUSE Linux Enterprise Micro 5.4 Affected

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EUVD-2026-63562 vulnerability details – vuln.today
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