CVE-2026-5731

CRITICALPre-NVD 9.89.8
EchelonGraph scoreMEDIUM confidence

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

Score 9.8 from GitHub Security Advisory (severity: CRITICAL) published 2026-04-07. CISA-ADP (Vulnrichment) CVSS v3.1 baseline 9.8; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: CISA-ADP (Vulnrichment) CVSS v3.1, EPSS, GitHub Security Advisory
Trending — 4 sources updated this week

Also known asEUVD-2026-19610 (ENISA EUVD) · GHSA-fwrw-mfrr-q8px (GitHub Security Advisories)Source: ENISA EUVD

9.8EG
EchelonGraph verdictPlan a fixRemediate within your standard update timelines (the SSVC decision on this page).
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0.3%CVSS: 9.8Exploit: None knownExposed services: Not assessed

A fix is available — apply it.

Memory safety bugs present in Firefox ESR 115.34.0, Firefox ESR 140.9.0, Thunderbird ESR 140.9.0, Firefox 149.0.1 and Thunderbird 149.0.1. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability was fixed in Firefox 149.0.2, Firefox ESR 115.34.1, Firefox ESR 140.9.1, Thunderbird 149.0.2, and Thunderbird 140.9.1.

CVSS v3
9.8
EG Score
9.8CRITICALmedium confidence
EG Risk
44
EG Risk 44/100

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)
Severity98% × 45%
Impact severity (EG Severity): CVSS 9.8 of 10. Never the KEV-floored or EPSS-lifted EG Score.
Exploitation0.3% × 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 low or medium mission impact; Track* at high (mission-essential systems).
Exploitation none (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact total (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.
EPSS PROB
0.3%
EPSS %ILE
27th
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 (9.8): severity, escalated by confirmed exploitation. This CVE's 9.8 is its impact severity (EG Severity), not escalated.

EG Severity
9.8 CRITICALCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.GitHub Security Advisory CVSS
EG Likelihood
0.3% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-10-29). 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 low or medium mission impact; Track* at high (mission-essential systems).CISA BOD 26-04: 14 days if the affected system is publicly exposed; Fix on system upgrade if it is not.Each input and its source: the SSVC and BOD 26-04 blocks below.

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

A fix is available. Apply it within your standard update timelines.

Exploitation none (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact total (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; Fix on system upgrade if it is not.

In CISA KEV no (CISA's KEV catalog) · Automatable no (CISA Vulnrichment) · Technical impact total (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

April 7, 2026

Last Modified

October 24, 2026

Advisory Details (10)

Auto-updated Oct 26, 2026
Patch available. Sources: redhat.
Red HatMentions a patch (unverified)

Affected: Red Hat Enterprise Linux 9.6 Extended Update Support.

https://access.redhat.com/errata/RHSA-2026:13342
Red HatMentions a patch (unverified)

Affected: Red Hat Enterprise Linux 9.0 Update Services for SAP Solutions.

https://access.redhat.com/errata/RHSA-2026:12264
Red HatMentions a patch (unverified)

Affected: Red Hat Enterprise Linux 10.0 Extended Update Support.

https://access.redhat.com/errata/RHSA-2026:11813
Red HatMentions a patch (unverified)

Affected: Red Hat Enterprise Linux 8.2 Advanced Update Support.

https://access.redhat.com/errata/RHSA-2026:11805
Web page

Security Vulnerabilities fixed in Thunderbird 140.9.1 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2026-29/
Web page

Security Vulnerabilities fixed in Thunderbird 149.0.2 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2026-28/
Web page

Security Vulnerabilities fixed in Firefox ESR 140.9.1 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2026-27/
Web page

Security Vulnerabilities fixed in Firefox ESR 115.34.1 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2026-26/
Web page

Security Vulnerabilities fixed in Firefox 149.0.2 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2026-25/

Patch Availability(24)

Vendor / EcosystemFix (by version range) / PatchReleasedSource
redhatthunderbird-0:140.9.1-1.el8_62026-05-11redhat
redhatfirefox-0:140.9.1-2.el7_92026-05-06redhat
redhatthunderbird-0:140.9.1-1.el8_42026-05-06redhat
redhatthunderbird-0:140.9.1-1.el8_82026-05-06redhat
redhatfirefox-0:140.9.1-1.el9_22026-05-06redhat
redhatfirefox-0:140.9.1-1.el9_42026-05-05redhat
redhatfirefox-0:140.9.1-1.el8_82026-05-05redhat
redhatfirefox-0:140.9.1-1.el10_02026-05-05redhat
redhatfirefox-0:140.9.1-1.el8_62026-05-05redhat
redhatfirefox-0:140.9.1-1.el9_02026-05-05redhat
redhatfirefox-0:140.9.1-1.el9_62026-05-05redhat
redhatfirefox-0:140.9.1-1.el8_42026-05-05redhat
redhatthunderbird-0:140.9.1-1.el9_22026-05-04redhat
redhatthunderbird-0:140.9.1-1.el9_62026-05-04redhat
redhatthunderbird-0:140.9.1-1.el9_42026-05-04redhat
redhatthunderbird-0:140.9.1-1.el9_02026-04-30redhat
redhatfirefox-0:140.9.1-1.el8_22026-04-29redhat
redhatthunderbird-0:140.9.1-1.el10_02026-04-29redhat
redhatthunderbird-0:140.9.1-1.el10_12026-04-22redhat
redhatthunderbird-0:140.9.1-1.el8_102026-04-21redhat
redhatthunderbird-0:140.9.1-1.el9_72026-04-16redhat
redhatfirefox-0:140.9.1-1.el8_102026-04-14redhat
redhatfirefox-0:140.9.1-1.el9_72026-04-13redhat
redhatfirefox-0:140.9.1-1.el10_12026-04-13redhat

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.

Affected Packages

(8 across 4 ecosystems)
Debian:11(2)
PackageVulnerable rangeFix by version rangeDependents
firefox-esr102.1.0esr-1 ... 91.9.1esr-1~deb9u1 (259 versions)
  • every version up to 140.9.1esr-1~deb11u1: fixed in 140.9.1esr-1~deb11u1
—
thunderbird1:102.0.1-1 ... 1:91.9.0-1~deb9u1 (310 versions)
  • every version up to 1:140.9.1esr-1~deb11u1: fixed in 1:140.9.1esr-1~deb11u1
—
Debian:12(2)
PackageVulnerable rangeFix by version rangeDependents
firefox-esr102.11.0esr-1 ... 140.9.1esr-1~deb11u1 (166 versions)
  • every version up to 140.9.1esr-1~deb12u1: fixed in 140.9.1esr-1~deb12u1
—
thunderbird1:102.11.0-1 ... 1:140.9.1esr-1~deb11u1 (195 versions)
  • every version up to 1:140.9.1esr-1~deb12u1: fixed in 1:140.9.1esr-1~deb12u1
—
Debian:13(2)
PackageVulnerable rangeFix by version rangeDependents
firefox-esr128.13.0esr-1 ... 140.9.1esr-1~deb12u1 (42 versions)
  • every version up to 140.9.1esr-1~deb13u1: fixed in 140.9.1esr-1~deb13u1
—
thunderbird1:128.13.0esr-1 ... 1:140.9.1esr-1~deb12u1 (51 versions)
  • every version up to 1:140.9.1esr-1~deb13u1: fixed in 1:140.9.1esr-1~deb13u1
—
Debian:14(2)
PackageVulnerable rangeFix by version rangeDependents
firefox-esr128.13.0esr-1 ... 140.9.1esr-1~deb13u1 (43 versions)
  • every version up to 140.9.1esr-1: fixed in 140.9.1esr-1
—
thunderbird1:128.13.0esr-1 ... 1:140.9.1esr-1~deb13u1 (52 versions)
  • every version up to 1:140.9.1esr-1: fixed in 1:140.9.1esr-1
—

Weakness Classification(2)

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

Additional Vendor Advisories

(4)

Data Freshness Timeline

(refreshed 31× in last 7d / 91× 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 388 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 288 oldest rows on record are not shown and were not checked, so the counts can still include repeats.

  1. 2026-10-30 03:22 UTCEG score recompute
  2. 2026-10-30 03:22 UTCVendor advisory
  3. 2026-10-30 03:22 UTCGHSA enrichmentGHSA-fwrw-mfrr-q8px · GitHub severity CRITICAL · GitHub CVSS 9.8
  4. 2026-10-29 16:33 UTCEPSS rescoreEPSS 0.3% · 27th percentile
  5. 2026-10-29 05:16 UTCEG score recompute
  6. 2026-10-29 05:16 UTCVendor advisory
  7. 2026-10-29 05:16 UTCGHSA enrichmentGHSA-fwrw-mfrr-q8px · GitHub severity CRITICAL · GitHub CVSS 9.8
  8. 2026-10-28 16:32 UTCEPSS rescoreEPSS 0.3% · 27th percentile
  9. 2026-10-28 07:09 UTCEG score recompute
  10. 2026-10-28 07:09 UTCVendor advisory
  11. 2026-10-28 07:09 UTCGHSA enrichmentGHSA-fwrw-mfrr-q8px · GitHub severity CRITICAL · GitHub CVSS 9.8
  12. 2026-10-27 16:32 UTCEPSS rescoreEPSS 0.3% · 27th percentile
  13. 2026-10-27 09:01 UTCEG score recompute
  14. 2026-10-27 09:01 UTCVendor advisory
  15. 2026-10-27 09:01 UTCGHSA enrichmentGHSA-fwrw-mfrr-q8px · GitHub severity CRITICAL · GitHub CVSS 9.8
  16. 2026-10-26 16:31 UTCEPSS rescoreEPSS 0.3% · 27th percentile
  17. 2026-10-26 09:42 UTCEG score recompute
  18. 2026-10-26 09:42 UTCVendor advisory
  19. 2026-10-26 09:42 UTCGHSA enrichmentGHSA-fwrw-mfrr-q8px · GitHub severity CRITICAL · GitHub CVSS 9.8
  20. 2026-10-25 16:33 UTCEPSS rescoreEPSS 0.3% · 27th percentile
  21. 2026-10-25 14:17 UTCEG score recompute
  22. 2026-10-25 11:35 UTCEG score recompute
  23. 2026-10-25 11:35 UTCVendor advisory
  24. 2026-10-25 11:35 UTCGHSA enrichmentGHSA-fwrw-mfrr-q8px · GitHub severity CRITICAL · GitHub CVSS 9.8
  25. 2026-10-24 16:33 UTCEPSS rescoreEPSS 0.6% · 48th percentile
Show 75 more
  1. 2026-10-24 13:26 UTCVendor advisory
  2. 2026-10-24 13:26 UTCGHSA enrichmentGHSA-fwrw-mfrr-q8px · GitHub severity CRITICAL · GitHub CVSS 9.8
  3. 2026-10-23 23:12 UTCEG score recompute
  4. 2026-10-23 23:12 UTCVendor advisory
  5. 2026-10-23 23:11 UTCGHSA enrichmentGHSA-fwrw-mfrr-q8px · GitHub severity CRITICAL · GitHub CVSS 9.8
  6. 2026-10-23 16:32 UTCEPSS rescoreEPSS 0.6% · 48th percentile
  7. 2026-10-23 00:48 UTCEG score recompute
  8. 2026-10-23 00:48 UTCVendor advisory
  9. 2026-10-23 00:48 UTCGHSA enrichmentGHSA-fwrw-mfrr-q8px · GitHub severity CRITICAL · GitHub CVSS 9.8
  10. 2026-10-22 16:34 UTCEPSS rescoreEPSS 0.6% · 48th percentile
  11. 2026-10-22 01:56 UTCEG score recompute
  12. 2026-10-22 01:56 UTCVendor advisory
  13. 2026-10-22 01:56 UTCGHSA enrichmentGHSA-fwrw-mfrr-q8px · GitHub severity CRITICAL · GitHub CVSS 9.8
  14. 2026-10-21 16:33 UTCEPSS rescoreEPSS 0.6% · 48th percentile
  15. 2026-10-21 03:49 UTCEG score recompute
  16. 2026-10-21 03:49 UTCVendor advisory
  17. 2026-10-21 03:49 UTCGHSA enrichmentGHSA-fwrw-mfrr-q8px · GitHub severity CRITICAL · GitHub CVSS 9.8
  18. 2026-10-20 16:33 UTCEPSS rescoreEPSS 0.6% · 48th percentile
  19. 2026-10-20 05:35 UTCEG score recompute
  20. 2026-10-20 05:35 UTCVendor advisory
  21. 2026-10-20 05:35 UTCGHSA enrichmentGHSA-fwrw-mfrr-q8px · GitHub severity CRITICAL · GitHub CVSS 9.8
  22. 2026-10-19 16:32 UTCEPSS rescoreEPSS 0.6% · 48th percentile
  23. 2026-10-19 07:07 UTCEG score recompute
  24. 2026-10-19 07:07 UTCVendor advisory
  25. 2026-10-19 07:07 UTCGHSA enrichmentGHSA-fwrw-mfrr-q8px · GitHub severity CRITICAL · GitHub CVSS 9.8
  26. 2026-10-18 08:56 UTCVendor advisory
  27. 2026-10-18 08:55 UTCGHSA enrichmentGHSA-fwrw-mfrr-q8px · GitHub severity CRITICAL · GitHub CVSS 9.8
  28. 2026-10-18 03:29 UTCEG score recompute
  29. 2026-10-17 16:35 UTCEPSS rescoreEPSS 0.6% · 48th percentile
  30. 2026-10-17 10:46 UTCEG score recompute
  31. 2026-10-17 10:46 UTCVendor advisory
  32. 2026-10-17 10:46 UTCGHSA enrichmentGHSA-fwrw-mfrr-q8px · GitHub severity CRITICAL · GitHub CVSS 9.8
  33. 2026-10-16 16:43 UTCEPSS rescoreEPSS 0.6% · 48th percentile
  34. 2026-10-16 12:23 UTCEG score recompute
  35. 2026-10-16 12:23 UTCVendor advisory
  36. 2026-10-16 12:23 UTCGHSA enrichmentGHSA-fwrw-mfrr-q8px · GitHub severity CRITICAL · GitHub CVSS 9.8
  37. 2026-10-15 16:32 UTCEPSS rescoreEPSS 0.6% · 48th percentile
  38. 2026-10-15 14:04 UTCEG score recompute
  39. 2026-10-15 14:04 UTCVendor advisory
  40. 2026-10-15 14:04 UTCGHSA enrichmentGHSA-fwrw-mfrr-q8px · GitHub severity CRITICAL · GitHub CVSS 9.8
  41. 2026-10-14 16:33 UTCEPSS rescoreEPSS 0.6% · 47th percentile
  42. 2026-10-14 08:51 UTCEG score recompute
  43. 2026-10-14 08:51 UTCVendor advisory
  44. 2026-10-14 08:51 UTCGHSA enrichmentGHSA-fwrw-mfrr-q8px · GitHub severity CRITICAL · GitHub CVSS 9.8
  45. 2026-10-13 16:34 UTCEPSS rescoreEPSS 0.6% · 47th percentile
  46. 2026-10-13 04:54 UTCEG score recompute
  47. 2026-10-13 04:54 UTCVendor advisory
  48. 2026-10-13 04:54 UTCGHSA enrichmentGHSA-fwrw-mfrr-q8px · GitHub severity CRITICAL · GitHub CVSS 9.8
  49. 2026-10-12 16:34 UTCEPSS rescoreEPSS 0.6% · 47th percentile
  50. 2026-10-12 15:54 UTCEG score recompute
  51. 2026-10-12 06:46 UTCVendor advisory
  52. 2026-10-12 06:45 UTCGHSA enrichmentGHSA-fwrw-mfrr-q8px · GitHub severity CRITICAL · GitHub CVSS 9.8
  53. 2026-10-11 19:37 UTCEG score recompute
  54. 2026-10-11 16:52 UTCEG score recompute
  55. 2026-10-11 14:15 UTCEG score recompute
  56. 2026-10-11 13:49 UTCEPSS rescoreEPSS 0.6% · 47th percentile
  57. 2026-10-10 20:00 UTCEPSS rescoreEPSS 0.6% · 47th percentile
  58. 2026-10-09 20:07 UTCEPSS rescoreEPSS 0.6% · 47th percentile
  59. 2026-10-08 17:13 UTCEPSS rescoreEPSS 0.6% · 47th percentile
  60. 2026-10-07 23:48 UTCEPSS rescoreEPSS 0.6% · 47th percentile
  61. 2026-10-06 15:18 UTCEPSS rescoreEPSS 0.6% · 47th percentile
  62. 2026-10-05 17:43 UTCEPSS rescoreEPSS 0.6% · 47th percentile
  63. 2026-10-04 23:22 UTCEPSS rescoreEPSS 0.6% · 47th percentile
  64. 2026-10-03 14:26 UTCEPSS rescoreEPSS 0.6% · 47th percentile
  65. 2026-10-02 17:56 UTCEPSS rescoreEPSS 0.6% · 47th percentile
  66. 2026-10-01 19:50 UTCEPSS rescoreEPSS 0.6% · 47th percentile
  67. 2026-09-30 15:03 UTCEPSS rescoreEPSS 0.6% · 47th percentile
  68. 2026-09-28 13:51 UTCEPSS rescoreEPSS 0.6% · 47th percentile
  69. 2026-09-26 15:59 UTCEPSS rescoreEPSS 0.6% · 47th percentile
  70. 2026-09-24 14:04 UTCEPSS rescoreEPSS 0.6% · 46th percentile
  71. 2026-09-23 17:54 UTCEPSS rescoreEPSS 0.3% · 27th percentile
  72. 2026-09-20 20:16 UTCEPSS rescoreEPSS 0.3% · 27th percentile
  73. 2026-09-18 19:28 UTCEPSS rescoreEPSS 0.3% · 27th percentile
  74. 2026-09-17 19:31 UTCEPSS rescoreEPSS 0.3% · 27th percentile
  75. 2026-09-16 14:08 UTCEPSS rescoreEPSS 0.3% · 27th percentile

Frequently asked(5)

What is CVE-2026-5731?
CVE-2026-5731 is a critical-severity vulnerability; its CVE record was published on April 7, 2026. Memory safety bugs present in Firefox ESR 115.34.0, Firefox ESR 140.9.0, Thunderbird ESR 140.9.0, Firefox 149.0.1 and Thunderbird 149.0.1. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code.…
When was the CVE record for CVE-2026-5731 published?
The CVE record for CVE-2026-5731 was published on April 7, 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 October 24, 2026; the record at its source may have been updated since.
Is CVE-2026-5731 actively exploited?
CVE-2026-5731 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.3% probability of exploitation in the next 30 days (27th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-5731?
CVE-2026-5731 has a CVSS v3.1 base score of 9.8 (CISA-ADP / Vulnrichment enrichment; NVD's own analysis pending).
How do I remediate CVE-2026-5731?
A fix for CVE-2026-5731 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2026-5731 are linked in the Vendor Advisories panel on this page.

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