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Vulnerability record · CVE-2026-63382 · published 20 August 2026

CVE-2026-63382: HTTP request smuggling vulnerability

Libevent is an event notification library. Prior to 2.1.13 and 2.2.2-alpha, the libevent evhttp parser in http.c inconsistently handles duplicate Transfer-Encoding headers, comma-separated Transfer-Encoding values, and bare line feeds in chunked framing. evhttp_find_header can select only the first header, evhttp_check_transfer_encoding_ was absent so the previous whole-string comparison fails to recognize valid lists ending in chunked, and evhttp_handle_chunked_read uses EVBUFFER_EOL_CRLF rather than EVBUFFER_EOL_CRLF_STRICT, accepting bare LF chunk terminators. When libevent is deployed behind a proxy that frames the same request differently, an unauthenticated remote attacker can desynchronize request boundaries and smuggle a second request, potentially bypassing access controls or poisoning caches. This issue is fixed in versions 2.1.13 and 2.2.2-alpha.

9.2 CVSS 4.0 Critical EPSS 0.78% · top 45.8% CWE-444 · HTTP request smuggling Awaiting Analysis
9.2CVSS 4.0 base score
0.78%EPSS exploitation probability, 30 days
NoNot in CISA KEV
0Affected product versions listed by NVD
8References
9 Sep 2026Last modified by NVD

Description

Libevent is an event notification library. Prior to 2.1.13 and 2.2.2-alpha, the libevent evhttp parser in http.c inconsistently handles duplicate Transfer-Encoding headers, comma-separated Transfer-Encoding values, and bare line feeds in chunked framing. evhttp_find_header can select only the first header, evhttp_check_transfer_encoding_ was absent so the previous whole-string comparison fails to recognize valid lists ending in chunked, and evhttp_handle_chunked_read uses EVBUFFER_EOL_CRLF rather than EVBUFFER_EOL_CRLF_STRICT, accepting bare LF chunk terminators. When libevent is deployed behind a proxy that frames the same request differently, an unauthenticated remote attacker can desynchronize request boundaries and smuggle a second request, potentially bypassing access controls or poisoning caches. This issue is fixed in versions 2.1.13 and 2.2.2-alpha.

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:L/SC:L/SI:L/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:

References

LinkTags
https://github.com/libevent/libevent/commit/10abb34b8dc3e1184de315dd261ce4b77563cda6
https://github.com/libevent/libevent/commit/5119ceb00557bf007f9065709e852686f3c0bb6e
https://github.com/libevent/libevent/commit/83ba67373032334559b82409db035dd8c3cc1660
https://github.com/libevent/libevent/commit/ac38703b2d312200c4f967f02936af0118d384a0
https://github.com/libevent/libevent/releases/tag/release-2.1.13-stable
https://github.com/libevent/libevent/releases/tag/release-2.2.2-alpha
https://github.com/libevent/libevent/security/advisories/GHSA-q39v-w2g7-gr8j
https://github.com/libevent/libevent/security/advisories/GHSA-q39v-w2g7-gr8j

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Source: NIST National Vulnerability Database (record CVE-2026-63382), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.