CVE-2026-63383

HIGHPre-NVD 8.78.7—
EchelonGraph scoreMEDIUM confidence

This high-severity CVE scores 8.7 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.4%, top 69% 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
Elevated
8.7EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 8.7Exploit: 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 can read beyond a contiguous evbuffer region in event_tagging.c when decode_tag_internal requests at most five bytes from evbuffer_pullup but iterates using the full logical buffer length. A fragmented evbuffer containing a six-byte malformed tag can therefore advance past the pullup window and trigger an out-of-bounds read, which can crash a process that decodes attacker-controlled tagged RPC data. This issue is fixed in versions 2.1.13 and 2.2.2-alpha.

CVSS v3
8.7
EG Score
8.7(medium)
EG Risk
70(Attend)
EG Risk 70/100SSVC: Attend

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
Severity87% × 45%
Exploitation40% × 40%
Automatability100% × 15%
Action: Remediate soon — notable exploitation risk.
EPSS PROB
0%
EPSS %ILE
31%
KEV
Not listed

Published

August 20, 2026

Last Modified

August 20, 2026

Advisory Details (5)

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

commit e1f9e21887c6 (libevent/libevent)

Patch available: libevent/libevent release-2.1.13-stable (contains commit e1f9e21887c6)

https://github.com/libevent/libevent/commit/e1f9e21887c6b104e206a718385ba3ffc75180cb
github_commit Patch Available

commit 91ed8745eeba (libevent/libevent)

Patch available: libevent/libevent release-2.2.2-alpha (contains commit 91ed8745eeba)

https://github.com/libevent/libevent/commit/91ed8745eebabdd27592a83d350338a8c4626321
github Patch Available🟡 PoC Available

decode_tag_internal() can lead to out-of-bounds read · Advisory · libevent/libevent · GitHub

https://github.com/libevent/libevent/security/advisories/GHSA-fj29-64w6-73h6

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 12× in last 7d / 20× 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. 2026-08-30 01:22 UTCEPSS rescore
  2. 2026-08-29 06:44 UTCEG score recompute
  3. 2026-08-28 21:42 UTCEPSS rescore
  4. 2026-08-27 15:36 UTCEG score recompute
  5. 2026-08-27 14:25 UTCEPSS rescore
  6. 2026-08-27 02:54 UTCEG score recompute
  7. 2026-08-26 14:46 UTCEPSS rescore
  8. 2026-08-26 01:38 UTCEG score recompute
  9. 2026-08-25 13:49 UTCEPSS rescore
  10. 2026-08-25 00:22 UTCEG score recompute
  11. 2026-08-24 11:43 UTCEG score recompute
  12. 2026-08-23 10:27 UTCEG score recompute
  13. 2026-08-23 00:19 UTCEPSS rescore
  14. 2026-08-22 09:12 UTCEG score recompute
  15. 2026-08-21 23:49 UTCEPSS rescore
  16. 2026-08-20 19:18 UTCEG score recompute
  17. 2026-08-20 18:52 UTCEG score recompute
  18. 2026-08-20 18:17 UTCEG score recompute
  19. 2026-08-20 17:57 UTCEG score recompute
  20. 2026-08-20 17:56 UTCMITRE cvelistV5first tracked

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Frequently asked(5)

What is CVE-2026-63383?
CVE-2026-63383 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 can read beyond a contiguous evbuffer region in eventtagging.c when decodetaginternal requests at most five bytes from evbufferpullup but iterates using the full logical buffer length. A fragmented evbuffer…
When was CVE-2026-63383 disclosed?
CVE-2026-63383 was first published in the National Vulnerability Database on August 20, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-63383 actively exploited?
CVE-2026-63383 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 68.7% of all scored CVEs.
What is the CVSS score of CVE-2026-63383?
CVE-2026-63383 has a CVSS v3 base score of 8.7 (NVD).
How do I remediate CVE-2026-63383?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-63383, 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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