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CVE-2026-63379— Libevent: HTTP Header smuggling

Quick assessment

Affected
libevent libevent
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

libevent 是一个事件通知库。在 2.1.13 及 2.2.2-alpha 之前的版本中，libevent 通过 函数处理 中的 HTTP 分块传输编码（chunked）响应尾部（trailers），并将这些尾部字段合并到请求头（request headers）中。修复方案引入了 函数以及一个临时的尾部头字段列表。未授权的远程攻击者可在尾部字段中嵌入安全敏感字段，从而导致上游代理服务器与 libevent 应用对有效头字段产生不同解释，进而引发请求走私（header smuggling）、授权绕过、代理头伪造

CVSS 6.3 · Medium EPSS 0.52% · P42

Affected Version Matrix 2

VendorProduct Version RangeStatus
libevent libevent < 2.1.13 affected
>= 2.2.0-alpha, < 2.2.2-alpha affected
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I. Basic Information for CVE-2026-63379

Vulnerability Information
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Vulnerability Title
Libevent: HTTP Header smuggling
Source: CVE Program / CVE List V5
Vulnerability Description
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.
Source: CVE Program / CVE List V5
CVSS Information
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
Source: CVE Program / CVE List V5
Vulnerability Type
HTTP请求的解释不一致性(HTTP请求私运)
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
libevent libevent < 2.1.13 -

II. Public POCs for CVE-2026-63379

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III. Intelligence Information for CVE-2026-63379

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Patches & Fixes for CVE-2026-63379 (2)

Vendor Advisories for CVE-2026-63379 (1)

Vendor Pages for CVE-2026-63379 (2)

Same Patch Batch · libevent · 2026-08-20 · 10 CVEs total

CVE-2026-63382 9.2 CRITICAL libevent evhttp: Multiple HTTP Parser Bugs Enable Request Smuggling
CVE-2026-63385 9.2 CRITICAL Libevent: HTTP header handling bugs create risk of access control bypass.
CVE-2026-63384 8.7 HIGH Libevent: `evtag_unmarshal_header()` decodes a wire `uint32` length into a signed `int` re
CVE-2026-63383 8.7 HIGH Libevent: decode_tag_internal() can lead to out-of-bounds read
CVE-2026-63388 8.4 HIGH Libevent: Heap out-of-bounds write in bufferevent_socket_set_conn_address_ reachable via A
CVE-2026-63495 7.5 HIGH Libevent: Unbounded memory accumulation in WebSocket server via fragmented frames
CVE-2026-63387 7.0 HIGH Libevent: Off-by-one stack buffer overflow in dnsname_to_labels via crafted DNS server res
CVE-2026-63381 5.8 MEDIUM Libevent: Dangling Pointer in `evbuffer_add_buffer_reference`
CVE-2026-63380 5.7 MEDIUM Libevent: Null Pointer Dereference in `evws_new_session`

IV. Related Vulnerabilities

Same product: libevent
Same vendor: libevent
Same weakness: CWE-444

V. Comments for CVE-2026-63379

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