CVE-2026-63387
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.
CSIRTS triage
- What
- Libevent contains an off-by-one stack buffer overflow in dnsname_to_labels when processing a crafted DNS server response.
- Who is affected
- Applications using Libevent for DNS resolution that accept responses from untrusted or compromised DNS servers.
- Urgency
- High severity (CVSS 7.0) and not yet exploited; promptly update DNS-dependent infrastructure.
- Action
- Upgrade Libevent to a patched version with corrected bounds checking in DNS name label parsing.
AI-assisted analysis generated from the source advisory — verify against the original.
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Exploitation outlook
- Low exploitation risk0.35% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 28% of all EPSS-scored CVEs.
Advisory coverage (2)
External references
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