# CVE-2026-63387

## Summary

- **CVE ID:** CVE-2026-63387
- **Severity:** HIGH
- **CVSS Score:** 7 (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H)
- **CWE:** CWE-121, CWE-193, CWE-787
- **Published:** Aug 20, 2026
- **Last Modified:** Aug 25, 2026

## 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.

## Affected Products

- libevent — libevent (>= 2.2.0-alpha, < 2.2.2-alpha)
- libevent — libevent (< 2.1.13)

## References

- [CNA](https://github.com/libevent/libevent/security/advisories/GHSA-58rx-7448-jw47)
- [CNA](https://github.com/libevent/libevent/releases/tag/release-2.1.13-stable)
- [CNA](https://github.com/libevent/libevent/releases/tag/release-2.2.2-alpha)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.34%
- **EPSS Percentile:** 27.6

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-11._