Libevent: Off-by-one stack buffer overflow in dnsname_to_labels via crafted DNS server response (CVE-2026-63387) | HOL Guard CVE

Unknown severity · Source severity not reportedCVE-2026-63387

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

Answer in brief

CVE-2026-63387 records a Unknown severity vulnerability in Libevent: Off-by-one stack buffer overflow in dnsname_to_labels via crafted DNS server response. The current sources do not mark it as known exploited. The current feed maps libevent/libevent (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Aug 20, 2026Updated Aug 20, 2026Source checked Aug 20, 2026First seen by HOL Aug 20, 2026Material review Aug 20, 2026

Upstream Advisory

Key facts

Risk: Unknown severitySource severity not reported
Exploitation: Not marked as known exploited
Affected software: 1 mapped package or product
Fix availability: Not reported

Why this deserves its current priority

A CVSS score is not reported in the current record. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps libevent/libevent (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
libevent/libeventgeneric	>= 2.2.0-alpha, < 2.2.2-alpha \|\| < 2.1.13	Not reported

Recommended response

Check inventory. Check lockfiles and deployed manifests for libevent/libevent.
Review the reported fix. Monitor this advisory for an available fix and review any installs of the affected package.

Evidence timeline and material changes

Published upstream
Aug 20, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Aug 20, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Aug 20, 2026

Sources and claim methodology

Upstream source 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.

Quoted source text, attributed separately from HOL analysis.