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CVE-2026-63387— Libevent: Off-by-one stack buffer overflow in dnsname_to_labels via crafted DNS server response

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2.2.0-alpha至2.2.2-alpha之前版本存在安全漏洞，该漏洞源于evdns.c中的off-by-one栈缓冲区溢出，dnsname_to_labels在格式化DNS记录时最终标签检查允许越界写入一个字节，包含PTR、CNAME、MX、NS或SOA数据的特制DNS服务器响应可触发该漏洞，导致进程崩溃或破坏。

CVSS 7.0 · High EPSS 0.42% · P34

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-2026-63387

Vulnerability Information
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Vulnerability Title
Libevent: Off-by-one stack buffer overflow in dnsname_to_labels via crafted DNS server response
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 has an off-by-one stack buffer overflow in evdns.c when dnsname_to_labels formats a name-bearing DNS record at the end of the 64 KB stack buffer allocated by evdns_server_request_format_response. The final-label check permits j plus label_len plus one to equal buf_len, after which the terminating null byte is written to buf[buf_len]. A crafted DNS server response containing PTR, CNAME, MX, NS, or SOA data can trigger the one-byte out-of-bounds write and crash or corrupt the process. This issue is fixed in versions 2.1.13 and 2.2.2-alpha.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
栈缓冲区溢出
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2.2.0-alpha至2.2.2-alpha之前版本存在安全漏洞，该漏洞源于evdns.c中的off-by-one栈缓冲区溢出，dnsname_to_labels在格式化DNS记录时最终标签检查允许越界写入一个字节，包含PTR、CNAME、MX、NS或SOA数据的特制DNS服务器响应可触发该漏洞，导致进程崩溃或破坏。
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-2026-63387

# POC Description Source Link Shenlong Link
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Qwen3.6-35B-A3B · 13840 chars
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III. Intelligence Information for CVE-2026-63387

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Vendor Advisories for CVE-2026-63387 (1)

Vendor Pages for CVE-2026-63387 (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-2026-63379 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-121

V. Comments for CVE-2026-63387

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