CVE-2026-63495

HIGHPre-NVD 7.57.5
EchelonGraph scoreMEDIUM confidence

“—” beside the score: it is equal to the CVSS score beside it.

This high-severity CVE scores 7.5 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.6% (47th percentile of EPSS-scored CVEs). No GitHub Security Advisory CVSS is on record for this CVE.

Triggered by: Headline CVSS from a secondary CVSS source
Sources: EPSS, a secondary CVSS source
Trending — 3 sources updated this weekElevated
7.5EG
EchelonGraph verdictPlan a fixRemediate within your standard update timelines at low or medium mission impact and sooner than that at high (the SSVC decision on this page).
  • CISA's Vulnrichment rates exploitation as PoC; EchelonGraph holds no exploit-code reference for it
CISA-KEV: Not listedEPSS PROB: 0.6%CVSS: 7.5Exploit: No code on recordExposed services: Not assessed

A fix is available — apply it.

Libevent is an event notification library. From 2.2.0-alpha-dev until 2.2.2-alpha, the libevent WebSocket server in ws.c accumulates fragmented frames in evws->incomplete_frames without enforcing a total message-size limit. An unauthenticated remote client can repeatedly send fragmented WebSocket frames below WS_MAX_RECV_FRAME_SZ with FIN=0, causing the evbuffer to grow without bound until the process or host exhausts memory. This issue is fixed in version 2.2.2-alpha.

CVSS v3
7.5
EG Score
7.5HIGHmedium confidence
EG Risk
65
EG Risk 65/100

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 (value × EchelonGraph’s weight)
Severity75% × 45%
The EG Score, 7.5 of 10.
Exploitation40% × 40%
EchelonGraph's fixed weight for EG-KEV Tier 3 (Elevated): a constant, not a probability.
Automatability100% × 15%
CISA's SSVC Automatable value: yes (Vulnrichment).
SSVC (CISA's decision table, applied by EchelonGraph): Track at low or medium mission impact; Attend at high (mission-essential systems).
Exploitation public PoC (CISA Vulnrichment) · Automatable yes (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE.
Action: A fix is available. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.
EPSS PROB
0.6%
EPSS %ILE
47th
KEV
Not listed

SSVC (CISA's decision table, applied by EchelonGraph)Track at low or medium mission impact; Attend at high (mission-essential systems).

A fix is available. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.

Exploitation public PoC (CISA Vulnrichment) · Automatable yes (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table

BOD 26-04 (CISA's remediation timeline, Table 1)14 days if the affected system is publicly exposed; 60 days if it is not.

In CISA KEV no (CISA's KEV catalog) · Automatable yes (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it

Published

August 20, 2026

Last Modified

September 9, 2026

Advisory Details (3)

Auto-updated Aug 20, 2026
Patch available. Sources: github, github_commit, 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 commit Patch Available

commit 291c4d1cd756 (libevent/libevent)

Patch available: libevent/libevent release-2.2.2-alpha (contains commit 291c4d1cd756)

https://github.com/libevent/libevent/commit/291c4d1cd75695e898030ebd5c4ddf26c094077b
GitHub advisoryMentions a patch (unverified)

Unbounded memory accumulation in WebSocket server via fragmented frames · Advisory · libevent/libevent · GitHub

https://github.com/libevent/libevent/security/advisories/GHSA-qx89-wf2v-vgmx

Vendor Advisories for CVE-2026-63495(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Patch Availability(1)

Vendor / EcosystemFix (by version range) / PatchReleasedSource
redhatlibevent-main-2.1.12-19.hum12026-07-17redhat

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

Weakness Classification(2)

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

Data Freshness Timeline

(refreshed 15× in last 7d / 94× in last 30d)

Each row is a time one of our pipelines fetched, updated or re-scored this CVE. 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. An arrow marks a change the record states ("CVSS v3 → 9.1"); EPSS and GHSA rows show the values recorded at that time, not what changed (EPSS values are rounded; hover one for the exact figures). Most recent first.

Showing the most recent 100 of 174 refreshes on record for this CVE.

A repeat, a row identical to one the same pipeline wrote less than 10 seconds earlier, is not a separate refresh and is not counted. None are among the latest 100 rows. The 74 oldest rows on record are not shown and were not checked, so the counts can still include repeats.

  1. 2026-10-13 16:34 UTCEPSS rescoreEPSS 0.6% · 47th percentile
  2. 2026-10-13 12:00 UTCEG score recompute
  3. 2026-10-13 12:00 UTCVendor advisory
  4. 2026-10-12 16:34 UTCEPSS rescoreEPSS 0.6% · 47th percentile
  5. 2026-10-12 15:49 UTCEG score recompute
  6. 2026-10-11 19:33 UTCEG score recompute
  7. 2026-10-11 16:48 UTCEG score recompute
  8. 2026-10-11 14:10 UTCEG score recompute
  9. 2026-10-11 13:49 UTCEPSS rescoreEPSS 0.6% · 47th percentile
  10. 2026-10-10 20:00 UTCEPSS rescoreEPSS 0.6% · 47th percentile
  11. 2026-10-09 20:07 UTCEPSS rescoreEPSS 0.6% · 47th percentile
  12. 2026-10-08 17:13 UTCEPSS rescoreEPSS 0.6% · 47th percentile
  13. 2026-10-08 05:22 UTCEG score recompute
  14. 2026-10-08 05:22 UTCVendor advisory
  15. 2026-10-07 23:48 UTCEPSS rescoreEPSS 0.6% · 47th percentile
  16. 2026-10-07 05:16 UTCVendor advisory
  17. 2026-10-06 16:53 UTCEG score recompute
  18. 2026-10-06 16:53 UTCVendor advisory
  19. 2026-10-06 15:18 UTCEPSS rescoreEPSS 0.6% · 47th percentile
  20. 2026-10-06 03:24 UTCVendor advisory
  21. 2026-10-06 03:24 UTCVendor advisory
  22. 2026-10-06 03:24 UTCEG score recompute
  23. 2026-10-06 03:24 UTCVendor advisory
  24. 2026-10-05 17:43 UTCEPSS rescoreEPSS 0.6% · 47th percentile
  25. 2026-10-05 09:29 UTCEG score recompute
Show 75 more
  1. 2026-10-05 09:29 UTCVendor advisory
  2. 2026-10-04 23:22 UTCEPSS rescoreEPSS 0.6% · 47th percentile
  3. 2026-10-04 20:52 UTCVendor advisory
  4. 2026-10-04 05:05 UTCVendor advisory
  5. 2026-10-03 16:47 UTCEG score recompute
  6. 2026-10-03 16:47 UTCVendor advisory
  7. 2026-10-03 14:26 UTCEPSS rescoreEPSS 0.6% · 47th percentile
  8. 2026-10-02 21:35 UTCEG score recompute
  9. 2026-10-02 21:35 UTCVendor advisory
  10. 2026-10-02 17:56 UTCEPSS rescoreEPSS 0.6% · 47th percentile
  11. 2026-10-02 09:24 UTCVendor advisory
  12. 2026-10-01 21:29 UTCEG score recompute
  13. 2026-10-01 21:29 UTCVendor advisory
  14. 2026-10-01 19:50 UTCEPSS rescoreEPSS 0.6% · 47th percentile
  15. 2026-10-01 08:26 UTCVendor advisory
  16. 2026-09-30 20:31 UTCEG score recompute
  17. 2026-09-30 20:31 UTCVendor advisory
  18. 2026-09-30 15:03 UTCEPSS rescoreEPSS 0.6% · 47th percentile
  19. 2026-09-30 08:13 UTCEG score recompute
  20. 2026-09-30 08:13 UTCVendor advisory
  21. 2026-09-29 04:04 UTCEG score recompute
  22. 2026-09-29 04:04 UTCVendor advisory
  23. 2026-09-28 16:00 UTCEG score recompute
  24. 2026-09-28 16:00 UTCVendor advisory
  25. 2026-09-28 13:51 UTCEPSS rescoreEPSS 0.6% · 47th percentile
  26. 2026-09-28 03:53 UTCVendor advisory
  27. 2026-09-27 15:57 UTCEG score recompute
  28. 2026-09-27 15:57 UTCVendor advisory
  29. 2026-09-27 03:01 UTCEG score recompute
  30. 2026-09-27 03:01 UTCVendor advisory
  31. 2026-09-26 15:59 UTCEPSS rescoreEPSS 0.6% · 47th percentile
  32. 2026-09-25 12:38 UTCVendor advisory
  33. 2026-09-25 00:41 UTCEG score recompute
  34. 2026-09-25 00:41 UTCVendor advisory
  35. 2026-09-24 11:30 UTCVendor advisory
  36. 2026-09-23 23:35 UTCEG score recompute
  37. 2026-09-23 23:35 UTCVendor advisory
  38. 2026-09-23 17:54 UTCEPSS rescoreEPSS 0.5% · 43rd percentile
  39. 2026-09-23 11:39 UTCVendor advisory
  40. 2026-09-22 23:43 UTCEG score recompute
  41. 2026-09-22 23:43 UTCVendor advisory
  42. 2026-09-22 11:46 UTCVendor advisory
  43. 2026-09-21 23:49 UTCEG score recompute
  44. 2026-09-21 23:49 UTCVendor advisory
  45. 2026-09-21 11:53 UTCVendor advisory
  46. 2026-09-20 23:57 UTCEG score recompute
  47. 2026-09-20 23:57 UTCVendor advisory
  48. 2026-09-20 20:16 UTCEPSS rescoreEPSS 0.5% · 42nd percentile
  49. 2026-09-20 12:01 UTCVendor advisory
  50. 2026-09-19 23:52 UTCEG score recompute
  51. 2026-09-19 23:52 UTCVendor advisory
  52. 2026-09-19 11:56 UTCVendor advisory
  53. 2026-09-19 00:00 UTCEG score recompute
  54. 2026-09-19 00:00 UTCVendor advisory
  55. 2026-09-18 19:28 UTCEPSS rescoreEPSS 0.5% · 42nd percentile
  56. 2026-09-18 12:04 UTCVendor advisory
  57. 2026-09-18 00:08 UTCEG score recompute
  58. 2026-09-18 00:08 UTCVendor advisory
  59. 2026-09-17 11:33 UTCVendor advisory
  60. 2026-09-16 23:36 UTCEG score recompute
  61. 2026-09-16 23:36 UTCVendor advisory
  62. 2026-09-16 14:08 UTCEPSS rescoreEPSS 0.5% · 42nd percentile
  63. 2026-09-16 11:40 UTCEG score recompute
  64. 2026-09-16 11:40 UTCVendor advisory
  65. 2026-09-16 05:15 UTCEPSS rescoreEPSS 0.5% · 42nd percentile
  66. 2026-09-15 23:41 UTCVendor advisory
  67. 2026-09-15 11:45 UTCEG score recompute
  68. 2026-09-15 11:45 UTCVendor advisory
  69. 2026-09-14 23:49 UTCVendor advisory
  70. 2026-09-14 11:07 UTCVendor advisory
  71. 2026-09-13 23:11 UTCEG score recompute
  72. 2026-09-13 23:11 UTCVendor advisory
  73. 2026-09-13 11:16 UTCVendor advisory
  74. 2026-09-12 23:20 UTCEG score recompute
  75. 2026-09-12 23:20 UTCVendor advisory

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Frequently asked(5)

What is CVE-2026-63495?
CVE-2026-63495 is a high-severity vulnerability; its CVE record was published on August 20, 2026. Libevent is an event notification library. From 2.2.0-alpha-dev until 2.2.2-alpha, the libevent WebSocket server in ws.c accumulates fragmented frames in evws->incompleteframes without enforcing a total message-size limit. An unauthenticated remote client can repeatedly send fragmented WebSocket…
When was the CVE record for CVE-2026-63495 published?
The CVE record for CVE-2026-63495 was published on August 20, 2026. That is the record's publication date; the vulnerability itself may have been made public earlier. EchelonGraph's copy of the record carries a last-modified date of September 9, 2026; the record at its source may have been updated since.
Is CVE-2026-63495 actively exploited?
CVE-2026-63495 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.6% probability of exploitation in the next 30 days (47th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-63495?
CVE-2026-63495 has a CVSS base score of 7.5 (a secondary CVSS source that NVD displays; NVD's own analysis pending).
How do I remediate CVE-2026-63495?
A fix for CVE-2026-63495 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2026-63495 are linked in the Vendor Advisories panel on this page.

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