CVE-2026-81666

MEDIUMPre-NVD 6.56.5
EchelonGraph scoreMEDIUM confidence

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

Score 6.5 from GitHub Security Advisory published 2026-09-04. A secondary CVSS source baseline 6.5; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: EPSS, GitHub Security Advisory, a secondary CVSS source

Also known asEUVD-2026-70987 (ENISA EUVD) · GHSA-8297-6g53-8gp5 (GitHub Security Advisories)Source: ENISA EUVD

6.5EG
EchelonGraph verdictMonitorNo fix is confirmed yet: check the vendor's advisory for a fixed release; until one is applied, restrict network exposure of the affected system or apply the vendor's mitigation on your normal schedule (the SSVC decision on this page).
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0.2%CVSS: 6.5Exploit: None knownExposed services: Not assessed

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

An integer overflow was found in Corosync's handling of membership commit token messages. The length-validation check for these messages can be bypassed on 32-bit systems due to an integer overflow in the calculation of the expected message length, allowing a crafted network packet to trigger an out-of-bounds memory access that crashes the Corosync daemon. This results in a denial of service for the affected cluster node. The overflow does not occur on 64-bit systems, where the length calculation is correctly performed in 64-bit arithmetic.

CVSS v3
6.5
EG Score
6.5MEDIUMmedium confidence
EG Risk
29
EG Risk 29/100

EG Risk is EchelonGraph's 0–100 priority score. It fuses impact severity (EG Severity, the CVSS base score, never the KEV-floored or EPSS-lifted EG Score) with real-world exploitation and automatability, under weights EchelonGraph set by hand, so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner.

How it’s computed (value × EchelonGraph’s weight)
Severity65% × 45%
Impact severity (EG Severity): CVSS 6.5 of 10. Never the KEV-floored or EPSS-lifted EG Score.
Exploitation0.2% × 40%
FIRST EPSS: the 30-day exploitation probability when EchelonGraph scored this CVE.
Automatability0% × 15%
CISA's SSVC Automatable value: no (Vulnrichment).
SSVC (CISA's decision table, applied by EchelonGraph): Track at every mission impact level.
Exploitation none (CISA Vulnrichment) · Automatable no (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: No fix is confirmed yet. Check the vendor's advisory for a fixed release; until one is applied, restrict network exposure of the affected system or apply the vendor's mitigation on your normal schedule.
EPSS PROB
0.2%
EPSS %ILE
15th
KEV
Not listed

What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)

The EG score (6.5): severity, escalated by confirmed exploitation. This CVE's 6.5 is its impact severity (EG Severity), not escalated.

EG Severity
6.5 MEDIUMCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.GitHub Security Advisory CVSS
EG Likelihood
0.2% within 30 daysSource: FIRST EPSS. FIRST's exploitation probability, not an EchelonGraph model.
Confirmed exploitation
None on record (CISA KEV, EG-KEV Tier 1)Reported apart from the likelihood: an observed fact, not a probability.
EG Priority
SSVC Track at medium mission impactTrack at every mission impact level.CISA BOD 26-04: 60 days if the affected system is publicly exposed; Fix on system upgrade if it is not.No released fix is confirmed on this page, but CISA's timeline does not wait for a fix's release: it starts when an agency identifies the flaw on an asset and updates the CDM Agency and Federal Dashboard, and the directive counts patching, decommissioning the system or another action as remediation. Until a fixed release is applied, mitigate as this page's verdict says. In the directive's words, “Fix on system upgrade” means that, “unless conditions change”, the vulnerability “should be remediated the next time the vulnerable asset receives a scheduled major upgrade or rebuild”: its timelines are “dynamic as facts change”, and a KEV listing shortens them.Each input and its source, and whom BOD 26-04 binds: the SSVC and BOD 26-04 blocks below.

SSVC (CISA's decision table, applied by EchelonGraph)Track at every mission impact level.

No fix is confirmed yet. Check the vendor's advisory for a fixed release; until one is applied, restrict network exposure of the affected system or apply the vendor's mitigation on your normal schedule.

Exploitation none (CISA Vulnrichment) · Automatable no (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)60 days if the affected system is publicly exposed; Fix on system upgrade if it is not.

No released fix is confirmed on this page, but CISA's timeline does not wait for a fix's release: it starts when an agency identifies the flaw on an asset and updates the CDM Agency and Federal Dashboard, and the directive counts patching, decommissioning the system or another action as remediation. Until a fixed release is applied, mitigate as this page's verdict says. In the directive's words, “Fix on system upgrade” means that, “unless conditions change”, the vulnerability “should be remediated the next time the vulnerable asset receives a scheduled major upgrade or rebuild”: its timelines are “dynamic as facts change”, and a KEV listing shortens them.

The score's inputs: In CISA KEV no (CISA's KEV catalog) · Automatable no (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

September 4, 2026

Last Modified

October 21, 2026

Advisory Details (2)

Auto-updated Sep 4, 2026
No fix on record yet. Sources: redhat.
Red Hat

2524923 – (CVE-2026-81666) CVE-2026-81666 corosync: corosync: integer overflow in check_memb_commit_token_sanity may bypass message length validation on 32-bit systems

https://bugzilla.redhat.com/show_bug.cgi?id=2524923
Red HatMentions a patch (unverified)

CVE-2026-81666 - Red Hat Customer Portal

Affected: Red Hat Enterprise Linux 8, 9, and 10 ship primarily 64-bit architectures (x86_64, aarch64), so this specific overflow mechani

https://access.redhat.com/security/cve/CVE-2026-81666

Vendor Advisories for CVE-2026-81666(1)

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

Affected Packages

(3 across 3 ecosystems)
Debian:12(1)
PackageVulnerable rangeFix by version rangeDependents
corosync3.1.10-1 ... 3.1.9-2 (12 versions)
  • every version on: no fix on record
—
Debian:13(1)
PackageVulnerable rangeFix by version rangeDependents
corosync3.1.10-1 ... 3.1.9-2+deb13u1 (6 versions)
  • every version on: no fix on record
—
Debian:14(1)
PackageVulnerable rangeFix by version rangeDependents
corosync3.1.10-1, 3.1.10-2, 3.1.10-3, 3.1.10-4, 3.1.9-2
  • every version on: no fix on record
—

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 7× in last 7d / 57× 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 143 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 43 oldest rows on record are not shown and were not checked, so the counts can still include repeats.

  1. 2026-11-01 16:35 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  2. 2026-10-31 16:33 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  3. 2026-10-30 16:35 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  4. 2026-10-29 16:34 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  5. 2026-10-28 16:33 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  6. 2026-10-27 16:32 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  7. 2026-10-26 16:32 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  8. 2026-10-25 16:34 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  9. 2026-10-25 13:58 UTCEG score recompute
  10. 2026-10-24 16:33 UTCEPSS rescoreEPSS 0.2% · 8th percentile
  11. 2026-10-23 16:32 UTCEPSS rescoreEPSS 0.2% · 8th percentile
  12. 2026-10-22 16:35 UTCEPSS rescoreEPSS 0.2% · 8th percentile
  13. 2026-10-21 21:35 UTCEG score recompute
  14. 2026-10-21 21:34 UTCGHSA enrichmentGHSA-8297-6g53-8gp5 · GitHub CVSS 6.5
  15. 2026-10-21 20:26 UTCEG score recompute
  16. 2026-10-21 20:26 UTCGHSA enrichmentGHSA-8297-6g53-8gp5 · GitHub CVSS 6.5
  17. 2026-10-21 18:26 UTCEG score recompute
  18. 2026-10-21 18:26 UTCGHSA enrichmentGHSA-8297-6g53-8gp5 · GitHub CVSS 6.5
  19. 2026-10-21 18:01 UTCEG score recompute
  20. 2026-10-21 18:01 UTCGHSA enrichmentGHSA-8297-6g53-8gp5 · GitHub CVSS 6.5
  21. 2026-10-21 16:34 UTCEPSS rescoreEPSS 0.2% · 8th percentile
  22. 2026-10-20 16:33 UTCEPSS rescoreEPSS 0.2% · 8th percentile
  23. 2026-10-19 16:33 UTCEPSS rescoreEPSS 0.2% · 8th percentile
  24. 2026-10-18 16:33 UTCEPSS rescoreEPSS 0.2% · 8th percentile
  25. 2026-10-18 03:09 UTCEG score recompute
Show 75 more
  1. 2026-10-17 16:35 UTCEPSS rescoreEPSS 0.2% · 8th percentile
  2. 2026-10-16 16:44 UTCEPSS rescoreEPSS 0.2% · 8th percentile
  3. 2026-10-15 16:33 UTCEPSS rescoreEPSS 0.2% · 8th percentile
  4. 2026-10-14 16:33 UTCEPSS rescoreEPSS 0.2% · 8th percentile
  5. 2026-10-13 16:35 UTCEPSS rescoreEPSS 0.2% · 8th percentile
  6. 2026-10-12 16:35 UTCEPSS rescoreEPSS 0.2% · 8th percentile
  7. 2026-10-12 14:56 UTCEG score recompute
  8. 2026-10-11 19:20 UTCEG score recompute
  9. 2026-10-11 16:37 UTCEG score recompute
  10. 2026-10-11 13:54 UTCEG score recompute
  11. 2026-10-11 13:49 UTCEPSS rescoreEPSS 0.2% · 8th percentile
  12. 2026-10-10 20:00 UTCEPSS rescoreEPSS 0.2% · 8th percentile
  13. 2026-10-09 23:25 UTCEG score recompute
  14. 2026-10-09 23:25 UTCGHSA enrichmentGHSA-8297-6g53-8gp5 · GitHub CVSS 6.5
  15. 2026-10-09 20:07 UTCEPSS rescoreEPSS 0.2% · 8th percentile
  16. 2026-10-09 01:17 UTCEG score recompute
  17. 2026-10-09 01:17 UTCGHSA enrichmentGHSA-8297-6g53-8gp5 · GitHub CVSS 6.5
  18. 2026-10-08 17:13 UTCEPSS rescoreEPSS 0.2% · 8th percentile
  19. 2026-10-07 23:48 UTCEPSS rescoreEPSS 0.2% · 8th percentile
  20. 2026-10-07 23:15 UTCGHSA enrichmentGHSA-8297-6g53-8gp5 · GitHub CVSS 6.5
  21. 2026-10-06 15:52 UTCEG score recompute
  22. 2026-10-06 15:52 UTCGHSA enrichmentGHSA-8297-6g53-8gp5 · GitHub CVSS 6.5
  23. 2026-10-06 15:18 UTCEPSS rescoreEPSS 0.2% · 7th percentile
  24. 2026-10-05 17:43 UTCEPSS rescoreEPSS 0.2% · 7th percentile
  25. 2026-10-05 17:37 UTCEG score recompute
  26. 2026-10-05 17:37 UTCGHSA enrichmentGHSA-8297-6g53-8gp5 · GitHub CVSS 6.5
  27. 2026-10-04 23:22 UTCEPSS rescoreEPSS 0.2% · 7th percentile
  28. 2026-10-04 19:29 UTCEG score recompute
  29. 2026-10-04 19:29 UTCGHSA enrichmentGHSA-8297-6g53-8gp5 · GitHub CVSS 6.5
  30. 2026-10-03 20:48 UTCEG score recompute
  31. 2026-10-03 20:48 UTCGHSA enrichmentGHSA-8297-6g53-8gp5 · GitHub CVSS 6.5
  32. 2026-10-03 14:26 UTCEPSS rescoreEPSS 0.2% · 7th percentile
  33. 2026-10-02 22:41 UTCEG score recompute
  34. 2026-10-02 22:40 UTCGHSA enrichmentGHSA-8297-6g53-8gp5 · GitHub CVSS 6.5
  35. 2026-10-02 17:57 UTCEPSS rescoreEPSS 0.2% · 7th percentile
  36. 2026-10-02 00:30 UTCEG score recompute
  37. 2026-10-02 00:30 UTCGHSA enrichmentGHSA-8297-6g53-8gp5 · GitHub CVSS 6.5
  38. 2026-10-01 19:50 UTCEPSS rescoreEPSS 0.2% · 7th percentile
  39. 2026-10-01 00:54 UTCEG score recompute
  40. 2026-10-01 00:54 UTCGHSA enrichmentGHSA-8297-6g53-8gp5 · GitHub CVSS 6.5
  41. 2026-09-30 15:04 UTCEPSS rescoreEPSS 0.2% · 7th percentile
  42. 2026-09-30 02:45 UTCEG score recompute
  43. 2026-09-30 02:45 UTCGHSA enrichmentGHSA-8297-6g53-8gp5 · GitHub CVSS 6.5
  44. 2026-09-29 03:11 UTCEG score recompute
  45. 2026-09-29 03:11 UTCGHSA enrichmentGHSA-8297-6g53-8gp5 · GitHub CVSS 6.5
  46. 2026-09-28 13:52 UTCEPSS rescoreEPSS 0.2% · 7th percentile
  47. 2026-09-28 04:55 UTCEG score recompute
  48. 2026-09-28 04:54 UTCGHSA enrichmentGHSA-8297-6g53-8gp5 · GitHub CVSS 6.5
  49. 2026-09-27 13:48 UTCEPSS rescoreEPSS 0.2% · 7th percentile
  50. 2026-09-27 06:47 UTCEG score recompute
  51. 2026-09-27 06:47 UTCGHSA enrichmentGHSA-8297-6g53-8gp5 · GitHub CVSS 6.5
  52. 2026-09-26 15:59 UTCEPSS rescoreEPSS 0.2% · 7th percentile
  53. 2026-09-26 08:39 UTCEG score recompute
  54. 2026-09-26 08:39 UTCGHSA enrichmentGHSA-8297-6g53-8gp5 · GitHub CVSS 6.5
  55. 2026-09-25 10:17 UTCEG score recompute
  56. 2026-09-25 10:17 UTCGHSA enrichmentGHSA-8297-6g53-8gp5 · GitHub CVSS 6.5
  57. 2026-09-24 14:04 UTCEPSS rescoreEPSS 0.3% · 21st percentile
  58. 2026-09-24 12:10 UTCEG score recompute
  59. 2026-09-24 12:10 UTCGHSA enrichmentGHSA-8297-6g53-8gp5 · GitHub CVSS 6.5
  60. 2026-09-23 17:54 UTCEPSS rescoreEPSS 0.3% · 19th percentile
  61. 2026-09-23 14:02 UTCEG score recompute
  62. 2026-09-23 14:01 UTCGHSA enrichmentGHSA-8297-6g53-8gp5 · GitHub CVSS 6.5
  63. 2026-09-22 16:01 UTCEPSS rescoreEPSS 0.3% · 19th percentile
  64. 2026-09-22 15:53 UTCEG score recompute
  65. 2026-09-22 15:53 UTCGHSA enrichmentGHSA-8297-6g53-8gp5 · GitHub CVSS 6.5
  66. 2026-09-21 21:09 UTCEPSS rescoreEPSS 0.3% · 19th percentile
  67. 2026-09-21 17:46 UTCEG score recompute
  68. 2026-09-21 17:46 UTCGHSA enrichmentGHSA-8297-6g53-8gp5 · GitHub CVSS 6.5
  69. 2026-09-20 20:16 UTCEPSS rescoreEPSS 0.3% · 19th percentile
  70. 2026-09-20 19:39 UTCGHSA enrichmentGHSA-8297-6g53-8gp5 · GitHub CVSS 6.5
  71. 2026-09-19 21:32 UTCEG score recompute
  72. 2026-09-19 21:32 UTCGHSA enrichmentGHSA-8297-6g53-8gp5 · GitHub CVSS 6.5
  73. 2026-09-18 23:24 UTCEG score recompute
  74. 2026-09-18 23:24 UTCGHSA enrichmentGHSA-8297-6g53-8gp5 · GitHub CVSS 6.5
  75. 2026-09-18 19:28 UTCEPSS rescoreEPSS 0.3% · 19th percentile

Frequently asked(5)

What is CVE-2026-81666?
CVE-2026-81666 is a medium-severity vulnerability; its CVE record was published on September 4, 2026. An integer overflow was found in Corosync's handling of membership commit token messages. The length-validation check for these messages can be bypassed on 32-bit systems due to an integer overflow in the calculation of the expected message length, allowing a crafted network packet to trigger an…
When was CVE-2026-81666 made public?
CVE-2026-81666 was made public on September 4, 2026: that is the date its CVE record's CNA, Red Hat, Inc., gives for when the vulnerability was made public. The CVE record itself was published on September 4, 2026. EchelonGraph's copy of the record carries a last-modified date of October 21, 2026; the record at its source may have been updated since.
Is CVE-2026-81666 actively exploited?
CVE-2026-81666 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.2% probability of exploitation in the next 30 days (15th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-81666?
CVE-2026-81666 has a CVSS base score of 6.5 (a secondary CVSS source that NVD displays; NVD's own analysis pending).
How do I remediate CVE-2026-81666?
No fix for CVE-2026-81666 is confirmed yet. Until one is published, restrict network exposure of the affected system or apply the vendor's mitigation — for example, keep it off the internet or limit it to trusted networks — and watch the vendor's advisory for the fix. The vendor advisories EchelonGraph has for CVE-2026-81666 are linked in the Vendor Advisories panel on this page.

Dependency Blast Radius

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