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CVE-2026-63383— Libevent: decode_tag_internal() can lead to out-of-bounds read

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libevent组织的一个提供事件通知机制的网络开发库。 libevent 2.1.13之前版本和2.2.2-alpha之前版本存在缓冲区错误漏洞，该漏洞源于event_tagging.c中decode_tag_internal请求至多五个字节但使用完整逻辑缓冲区长度迭代，可能导致越界读取并使解码攻击者控制的标记RPC数据的进程崩溃。

CVSS 8.7 · High EPSS 0.49% · P40

Possible ATT&CK Techniques 1 AI

T1203 · Exploitation for Client Execution

Affected Version Matrix 2

VendorProduct Version RangeStatus
libevent libevent >= 2.2.0-alpha, < 2.2.2-alpha affected
< 2.1.13 affected
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I. Basic Information for CVE-2026-63383

Vulnerability Information
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Vulnerability Title
Libevent: decode_tag_internal() can lead to out-of-bounds read
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 can read beyond a contiguous evbuffer region in event_tagging.c when decode_tag_internal requests at most five bytes from evbuffer_pullup but iterates using the full logical buffer length. A fragmented evbuffer containing a six-byte malformed tag can therefore advance past the pullup window and trigger an out-of-bounds read, which can crash a process that decodes attacker-controlled tagged RPC data. 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:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
Source: CVE Program / CVE List V5
Vulnerability Type
跨界内存读
Source: CVE Program / CVE List V5
Vulnerability Title
libevent 缓冲区错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Libevent是libevent组织的一个提供事件通知机制的网络开发库。 libevent 2.1.13之前版本和2.2.2-alpha之前版本存在缓冲区错误漏洞，该漏洞源于event_tagging.c中decode_tag_internal请求至多五个字节但使用完整逻辑缓冲区长度迭代，可能导致越界读取并使解码攻击者控制的标记RPC数据的进程崩溃。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

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

II. Public POCs for CVE-2026-63383

# POC Description Source Link Shenlong Link
AI-Generated POC Verified env Premium
Reproduced successfully in a real sandbox · Below is the actual recording of building the environment and exploiting the vulnerability.
Success marker: VULNERABLE: ASAN heap-buffer-overflow (read size 1) in decode_tag_internal (CVE-2026-63383) [trigger] OOB read reached planted token: PROOF_1cfbbdaa02b635b3
Reproduction recording is a Pro+ exclusive
Watch the full sandbox build + live exploit recording for this CVE. Limited-time ¥499/mo.
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claude_code · 14101 chars
GitHub 复现环境（可 clone 直接跑）
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III. Intelligence Information for CVE-2026-63383

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Patches & Fixes for CVE-2026-63383 (2)

Vendor Advisories for CVE-2026-63383 (1)

Vendor Pages for CVE-2026-63383 (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-2026-63388 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-2026-63379 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-125

V. Comments for CVE-2026-63383

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