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CVE-2026-63495— Libevent: Unbounded memory accumulation in WebSocket server via fragmented frames

Quick assessment

Affected
libevent libevent
Exploitation
Public or AI PoC available; prioritize validation
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。从 2.2.0-alpha-dev 到 2.2.2-alpha 版本期间，libevent 的 WebSocket 服务器（在 ws.c 中实现）在将碎片化帧累积到 evws->incomplete_frames 时，未对总消息大小实施限制。未经身份验证的远程客户端可以反复发送 FIN=0 且长度低于 WS_MAX_RECV_FRAME_SZ 的 WebSocket 碎片帧，导致 evbuffer 不断膨胀，直至进程或主机内存耗尽。该问题已在 2.2.2-alpha 版本中得到修

CVSS 7.5 · High EPSS 0.43% · P35

Possible ATT&CK Techniques 1 AI

T1499 · Endpoint Denial of Service

Affected Version Matrix 1

VendorProduct Version RangeStatus
libevent libevent >= 2.2.0-alpha-dev, < 2.2.2-alpha affected
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I. Basic Information for CVE-2026-63495

Vulnerability Information
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Vulnerability Title
Libevent: Unbounded memory accumulation in WebSocket server via fragmented frames
Source: CVE Program / CVE List V5
Vulnerability Description
Libevent is an event notification library. From 2.2.0-alpha-dev until 2.2.2-alpha, the libevent WebSocket server in ws.c accumulates fragmented frames in evws->incomplete_frames without enforcing a total message-size limit. An unauthenticated remote client can repeatedly send fragmented WebSocket frames below WS_MAX_RECV_FRAME_SZ with FIN=0, causing the evbuffer to grow without bound until the process or host exhausts memory. This issue is fixed in version 2.2.2-alpha.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
未加控制的资源消耗(资源穷尽)
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
libevent libevent >= 2.2.0-alpha-dev, < 2.2.2-alpha -

II. Public POCs for CVE-2026-63495

# POC Description Source Link Shenlong Link
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Qwen3.6-35B-A3B · 10215 chars
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III. Intelligence Information for CVE-2026-63495

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Patches & Fixes for CVE-2026-63495 (1)

Vendor Advisories for CVE-2026-63495 (1)

Vendor Pages for CVE-2026-63495 (1)

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-2026-63387 7.0 HIGH Libevent: Off-by-one stack buffer overflow in dnsname_to_labels via crafted DNS server res
CVE-2026-63379 6.3 MEDIUM Libevent: HTTP Header smuggling
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-400

V. Comments for CVE-2026-63495

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