Buffer overflow in Libevent
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.
Vulnerability class: Buffer Overflow
CVSS v3 metric
CVSS v3 base score 7.0 (High). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H.
Affected products
- Libevent — versions < 2.1.13, >= 2.2.0-alpha, < 2.2.2-alpha
Weakness classification (CWE)
References
- security-advisories@github.com (x_refsource_CONFIRM)
- security-advisories@github.com (x_refsource_MISC)
- security-advisories@github.com (x_refsource_MISC)
Frequently asked questions
- What is CVE-2026-63387?
- CVE-2026-63387 is a high-severity vulnerability in Libevent, classified under Stack-based Buffer Overflow. CVSS score: 7.0/10. Published 2026-08-20.
- How severe is CVE-2026-63387?
- High severity. CVSS v3 base score is 7.0 out of 10.