CVE-2026-63387

HIGHPre-NVD 7.07.0—
EchelonGraph scoreMEDIUM confidence

This high-severity CVE scores 7.0 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.3%, top 73% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, secondary
Trending — 3 sources updated this weekElevated
7.0EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 7.0Exploit: Elevated riskExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

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.

CVSS v3
7.0
EG Score
7.0(medium)
EG Risk
48(Track)
EG Risk 48/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity70% × 45%
Exploitation40% × 40%
Automatability0% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
27%
KEV
Not listed

Published

August 20, 2026

Last Modified

August 25, 2026

Advisory Details (3)

Auto-updated Aug 20, 2026
🔬 Proof of concept available. Patch available. Sources: github, github_release.
github_release Patch Available

Libevent 2.2.2-alpha

Patch available: libevent/libevent release-2.2.2-alpha

https://github.com/libevent/libevent/releases/tag/release-2.2.2-alpha
github_release Patch Available

Libevent 2.1.13-stable

Patch available: libevent/libevent release-2.1.13-stable

https://github.com/libevent/libevent/releases/tag/release-2.1.13-stable
github Patch Available🟡 PoC Available

Off-by-one stack buffer overflow in dnsname_to_labels via crafted DNS server response · Advisory · libevent/libevent · GitHub

https://github.com/libevent/libevent/security/advisories/GHSA-58rx-7448-jw47

Weakness Classification(3)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 12× in last 7d / 12× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-08-25 16:26 UTCEG score recompute
  2. 2026-08-25 15:16 UTCEG score recompute
  3. 2026-08-25 13:49 UTCEPSS rescore
  4. 2026-08-25 02:15 UTCEG score recompute
  5. 2026-08-24 13:15 UTCEG score recompute
  6. 2026-08-23 11:16 UTCEG score recompute
  7. 2026-08-23 00:19 UTCEPSS rescore
  8. 2026-08-22 09:17 UTCEG score recompute
  9. 2026-08-21 23:49 UTCEPSS rescore
  10. 2026-08-20 18:17 UTCEG score recompute
  11. 2026-08-20 17:57 UTCEG score recompute
  12. 2026-08-20 17:56 UTCMITRE cvelistV5first tracked

Frequently asked(5)

What is CVE-2026-63387?
CVE-2026-63387 is a high vulnerability published on August 20, 2026. 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 dnsnametolabels formats a name-bearing DNS record at the end of the 64 KB stack buffer allocated by evdnsserverrequestformatresponse. The final-label check…
When was CVE-2026-63387 disclosed?
CVE-2026-63387 was first published in the National Vulnerability Database on August 20, 2026, with the most recent update on August 25, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-63387 actively exploited?
CVE-2026-63387 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 72.9% of all scored CVEs.
What is the CVSS score of CVE-2026-63387?
CVE-2026-63387 has a CVSS v3 base score of 7.0 (NVD).
How do I remediate CVE-2026-63387?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-63387, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

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