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

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-63387
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-08-20 18:16:36 UTC
Updated2026-08-20 18:16:36 UTC
DescriptionLibevent 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.

Risk And Classification

Primary CVSS: v3.1 7 HIGH from [email protected]

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H

Problem Types: CWE-121 | CWE-193 | CWE-787 | CWE-121 CWE-121: Stack-based Buffer Overflow | CWE-193 CWE-193: Off-by-one Error | CWE-787 CWE-787: Out-of-bounds Write

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary7HIGHCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H
3.1CNADECLARED7HIGHCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
Low
Availability
High

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Libevent Libevent affected >= 2.2.0-alpha, < 2.2.2-alpha Not specified
CNA Libevent Libevent affected < 2.1.13 Not specified

References

ReferenceSourceLinkTags
github.com/libevent/libevent/security/advisories/GHSA-58rx-7448-jw47 [email protected] github.com
github.com/libevent/libevent/releases/tag/release-2.1.13-stable [email protected] github.com
github.com/libevent/libevent/releases/tag/release-2.2.2-alpha [email protected] github.com
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