CVE-2026-4720

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 2026-03-24. 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

Also known asEUVD-2026-14855 (ENISA EUVD) · GHSA-h6r3-p5gv-5qgc (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: 0.4%CVSS: 9.8Exploit: None knownExposed services: Not assessed

A fix is available — apply it.

Memory safety bugs present in Firefox ESR 140.8, Thunderbird ESR 140.8, Firefox 148 and Thunderbird 148. 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, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.

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.
Exploitation0.4% × 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
0.4%
EPSS %ILE
39th
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
0.4% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-11-12). 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, and whom BOD 26-04 binds: 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.

The score's inputs: 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

March 24, 2026

Last Modified

July 15, 2026

Advisory Details (10)

Auto-updated Oct 31, 2026
Patch available. Sources: redhat.
Red HatMentions a patch (unverified)

Affected: Red Hat Enterprise Linux 10.

https://access.redhat.com/errata/RHSA-2026:6342
Red HatMentions a patch (unverified)

Affected: Red Hat Enterprise Linux 9.

https://access.redhat.com/errata/RHSA-2026:6188
Red HatMentions a patch (unverified)

Affected: Red Hat Enterprise Linux 8.

https://access.redhat.com/errata/RHSA-2026:5932
Red HatMentions a patch (unverified)

Affected: Red Hat Enterprise Linux 10.

https://access.redhat.com/errata/RHSA-2026:5931
Red HatMentions a patch (unverified)

Affected: Red Hat Enterprise Linux 9.

https://access.redhat.com/errata/RHSA-2026:5930
Web page

Security Vulnerabilities fixed in Thunderbird 140.9 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2026-24/
Web page

Security Vulnerabilities fixed in Thunderbird 149 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2026-23/
Web page

Security Vulnerabilities fixed in Firefox ESR 140.9 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2026-22/
Web page

Security Vulnerabilities fixed in Firefox 149 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2026-20/

Patch Availability(25)

Vendor / EcosystemFix (by version range) / PatchReleasedSource
redhatthunderbird-0:140.9.0-1.el8_42026-04-20redhat
redhatfirefox-0:140.9.0-1.el7_92026-04-16redhat
redhatthunderbird-0:140.9.0-1.el8_62026-04-15redhat
redhatthunderbird-0:140.9.0-1.el9_42026-04-15redhat
redhatthunderbird-0:140.9.0-1.el9_02026-04-15redhat
redhatthunderbird-0:140.9.0-1.el10_02026-04-15redhat
redhatthunderbird-0:140.9.0-1.el9_22026-04-15redhat
redhatthunderbird-0:140.9.0-1.el8_82026-04-15redhat
redhatthunderbird-0:140.9.0-1.el8_22026-04-15redhat
redhatthunderbird-0:140.9.0-1.el9_62026-04-15redhat
redhatfirefox-0:140.9.0-1.el8_22026-04-13redhat
redhatfirefox-0:140.9.0-1.el9_22026-04-13redhat
redhatfirefox-0:140.9.0-1.el8_42026-04-13redhat
redhatfirefox-0:140.9.0-1.el9_42026-04-13redhat
redhatfirefox-0:140.9.0-1.el8_82026-04-13redhat
redhatfirefox-0:140.9.0-1.el10_02026-04-13redhat
redhatfirefox-0:140.9.0-1.el9_02026-04-13redhat
redhatfirefox-0:140.9.0-1.el8_62026-04-13redhat
redhatfirefox-0:140.9.0-1.el9_62026-04-13redhat
redhatthunderbird-0:140.9.0-1.el8_102026-04-07redhat
redhatthunderbird-0:140.9.0-1.el10_12026-04-01redhat
redhatthunderbird-0:140.9.0-1.el9_72026-03-30redhat
redhatfirefox-0:140.9.0-1.el9_72026-03-26redhat
redhatfirefox-0:140.9.0-1.el10_12026-03-26redhat
redhatfirefox-0:140.9.0-1.el8_102026-03-26redhat

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 (255 versions)
  • every version up to 140.9.0esr-1~deb11u1: fixed in 140.9.0esr-1~deb11u1
—
thunderbird1:102.0.1-1 ... 1:91.9.0-1~deb9u1 (306 versions)
  • every version up to 1:140.9.0esr-1~deb11u1: fixed in 1:140.9.0esr-1~deb11u1
—
Debian:12(2)
PackageVulnerable rangeFix by version rangeDependents
firefox-esr102.11.0esr-1 ... 140.8.0esr-1~deb13u1 (161 versions)
  • every version up to 140.9.0esr-1~deb12u1: fixed in 140.9.0esr-1~deb12u1
—
thunderbird1:102.11.0-1 ... 1:140.9.0esr-1~deb11u1 (191 versions)
  • every version up to 1:140.9.0esr-1~deb12u1: fixed in 1:140.9.0esr-1~deb12u1
—
Debian:13(2)
PackageVulnerable rangeFix by version rangeDependents
firefox-esr128.13.0esr-1 ... 140.8.0esr-1~deb13u1 (36 versions)
  • every version up to 140.9.0esr-1~deb13u1: fixed in 140.9.0esr-1~deb13u1
—
thunderbird1:128.13.0esr-1 ... 1:140.9.0esr-1~deb11u1 (46 versions)
  • every version up to 1:140.9.0esr-1~deb13u1: fixed in 1:140.9.0esr-1~deb13u1
—
Debian:14(2)
PackageVulnerable rangeFix by version rangeDependents
firefox-esr128.13.0esr-1 ... 140.9.0esr-1~deb13u1 (39 versions)
  • every version up to 140.9.0esr-1: fixed in 140.9.0esr-1
—
thunderbird1:128.13.0esr-1 ... 1:140.9.0esr-1~deb13u1 (48 versions)
  • every version up to 1:140.9.0esr-1: fixed in 1:140.9.0esr-1
—

Weakness Classification(1)

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

Additional Vendor Advisories

(5)

Data Freshness Timeline

(refreshed 20× in last 7d / 93× 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 its CVE.org record (CNA or CISA ADP). 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). "EchelonGraph re-scored" is our own recompute of this CVE's score, not an update from a source, and is not counted in the refreshes above. Most recent first.

Showing the most recent 100 of 405 rows 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 305 oldest rows on record are not shown and were not checked, so the counts can still include repeats.

  1. 2026-11-12 22:43 UTCEchelonGraph re-scored
  2. 2026-11-12 22:43 UTCVendor advisory
  3. 2026-11-12 22:43 UTCGHSA enrichmentGHSA-h6r3-p5gv-5qgc · GitHub severity CRITICAL · GitHub CVSS 9.8
  4. 2026-11-12 16:34 UTCEPSS rescoreEPSS 0.4% · 39th percentile
  5. 2026-11-12 00:43 UTCEchelonGraph re-scored
  6. 2026-11-12 00:43 UTCVendor advisory
  7. 2026-11-12 00:43 UTCGHSA enrichmentGHSA-h6r3-p5gv-5qgc · GitHub severity CRITICAL · GitHub CVSS 9.8
  8. 2026-11-11 16:39 UTCEPSS rescoreEPSS 0.4% · 39th percentile
  9. 2026-11-11 02:55 UTCEchelonGraph re-scored
  10. 2026-11-11 02:55 UTCVendor advisory
  11. 2026-11-11 02:55 UTCGHSA enrichmentGHSA-h6r3-p5gv-5qgc · GitHub severity CRITICAL · GitHub CVSS 9.8
  12. 2026-11-10 16:44 UTCEPSS rescoreEPSS 0.4% · 39th percentile
  13. 2026-11-10 05:00 UTCEchelonGraph re-scored
  14. 2026-11-10 05:00 UTCVendor advisory
  15. 2026-11-10 05:00 UTCGHSA enrichmentGHSA-h6r3-p5gv-5qgc · GitHub severity CRITICAL · GitHub CVSS 9.8
  16. 2026-11-09 16:35 UTCEPSS rescoreEPSS 0.4% · 38th percentile
  17. 2026-11-09 07:13 UTCEchelonGraph re-scored
  18. 2026-11-09 07:13 UTCVendor advisory
  19. 2026-11-09 07:13 UTCGHSA enrichmentGHSA-h6r3-p5gv-5qgc · GitHub severity CRITICAL · GitHub CVSS 9.8
  20. 2026-11-08 16:39 UTCEPSS rescoreEPSS 0.4% · 38th percentile
  21. 2026-11-08 09:23 UTCEchelonGraph re-scored
  22. 2026-11-08 09:23 UTCVendor advisory
  23. 2026-11-08 09:23 UTCGHSA enrichmentGHSA-h6r3-p5gv-5qgc · GitHub severity CRITICAL · GitHub CVSS 9.8
  24. 2026-11-07 16:39 UTCEPSS rescoreEPSS 0.4% · 38th percentile
  25. 2026-11-07 11:36 UTCEchelonGraph re-scored
Show 75 more
  1. 2026-11-07 11:36 UTCGHSA enrichmentGHSA-h6r3-p5gv-5qgc · GitHub severity CRITICAL · GitHub CVSS 9.8
  2. 2026-11-06 16:38 UTCEPSS rescoreEPSS 0.4% · 38th percentile
  3. 2026-11-06 13:48 UTCEchelonGraph re-scored
  4. 2026-11-06 13:48 UTCVendor advisory
  5. 2026-11-06 13:48 UTCGHSA enrichmentGHSA-h6r3-p5gv-5qgc · GitHub severity CRITICAL · GitHub CVSS 9.8
  6. 2026-11-05 16:38 UTCEPSS rescoreEPSS 0.4% · 38th percentile
  7. 2026-11-05 16:01 UTCVendor advisory
  8. 2026-11-05 16:01 UTCGHSA enrichmentGHSA-h6r3-p5gv-5qgc · GitHub severity CRITICAL · GitHub CVSS 9.8
  9. 2026-11-04 18:13 UTCEchelonGraph re-scored
  10. 2026-11-04 18:13 UTCVendor advisory
  11. 2026-11-04 18:13 UTCGHSA enrichmentGHSA-h6r3-p5gv-5qgc · GitHub severity CRITICAL · GitHub CVSS 9.8
  12. 2026-11-04 16:35 UTCEPSS rescoreEPSS 0.4% · 38th percentile
  13. 2026-11-03 20:25 UTCEchelonGraph re-scored
  14. 2026-11-03 20:25 UTCVendor advisory
  15. 2026-11-03 20:25 UTCGHSA enrichmentGHSA-h6r3-p5gv-5qgc · GitHub severity CRITICAL · GitHub CVSS 9.8
  16. 2026-11-03 16:48 UTCEPSS rescoreEPSS 0.4% · 38th percentile
  17. 2026-11-02 22:38 UTCEchelonGraph re-scored
  18. 2026-11-02 22:38 UTCVendor advisory
  19. 2026-11-02 22:38 UTCGHSA enrichmentGHSA-h6r3-p5gv-5qgc · GitHub severity CRITICAL · GitHub CVSS 9.8
  20. 2026-11-02 16:45 UTCEPSS rescoreEPSS 0.4% · 38th percentile
  21. 2026-11-02 00:38 UTCEchelonGraph re-scored
  22. 2026-11-02 00:38 UTCVendor advisory
  23. 2026-11-02 00:38 UTCGHSA enrichmentGHSA-h6r3-p5gv-5qgc · GitHub severity CRITICAL · GitHub CVSS 9.8
  24. 2026-11-01 16:34 UTCEPSS rescoreEPSS 0.4% · 38th percentile
  25. 2026-11-01 02:51 UTCEchelonGraph re-scored
  26. 2026-11-01 02:51 UTCVendor advisory
  27. 2026-11-01 02:50 UTCGHSA enrichmentGHSA-h6r3-p5gv-5qgc · GitHub severity CRITICAL · GitHub CVSS 9.8
  28. 2026-10-31 16:33 UTCEPSS rescoreEPSS 0.4% · 38th percentile
  29. 2026-10-31 05:03 UTCEchelonGraph re-scored
  30. 2026-10-31 05:03 UTCVendor advisory
  31. 2026-10-31 05:03 UTCGHSA enrichmentGHSA-h6r3-p5gv-5qgc · GitHub severity CRITICAL · GitHub CVSS 9.8
  32. 2026-10-30 16:34 UTCEPSS rescoreEPSS 0.4% · 38th percentile
  33. 2026-10-30 07:15 UTCEchelonGraph re-scored
  34. 2026-10-30 07:15 UTCVendor advisory
  35. 2026-10-30 07:15 UTCGHSA enrichmentGHSA-h6r3-p5gv-5qgc · GitHub severity CRITICAL · GitHub CVSS 9.8
  36. 2026-10-29 16:33 UTCEPSS rescoreEPSS 0.4% · 38th percentile
  37. 2026-10-29 09:27 UTCEchelonGraph re-scored
  38. 2026-10-29 09:27 UTCVendor advisory
  39. 2026-10-29 09:27 UTCGHSA enrichmentGHSA-h6r3-p5gv-5qgc · GitHub severity CRITICAL · GitHub CVSS 9.8
  40. 2026-10-28 16:32 UTCEPSS rescoreEPSS 0.4% · 38th percentile
  41. 2026-10-28 11:39 UTCEchelonGraph re-scored
  42. 2026-10-28 11:39 UTCVendor advisory
  43. 2026-10-28 11:39 UTCGHSA enrichmentGHSA-h6r3-p5gv-5qgc · GitHub severity CRITICAL · GitHub CVSS 9.8
  44. 2026-10-27 16:32 UTCEPSS rescoreEPSS 0.4% · 38th percentile
  45. 2026-10-27 13:35 UTCEchelonGraph re-scored
  46. 2026-10-27 13:35 UTCVendor advisory
  47. 2026-10-27 13:35 UTCGHSA enrichmentGHSA-h6r3-p5gv-5qgc · GitHub severity CRITICAL · GitHub CVSS 9.8
  48. 2026-10-26 16:31 UTCEPSS rescoreEPSS 0.4% · 38th percentile
  49. 2026-10-26 15:18 UTCEchelonGraph re-scored
  50. 2026-10-26 15:18 UTCVendor advisory
  51. 2026-10-26 15:18 UTCGHSA enrichmentGHSA-h6r3-p5gv-5qgc · GitHub severity CRITICAL · GitHub CVSS 9.8
  52. 2026-10-25 16:33 UTCEPSS rescoreEPSS 0.4% · 37th percentile
  53. 2026-10-25 16:32 UTCVendor advisory
  54. 2026-10-25 16:31 UTCGHSA enrichmentGHSA-h6r3-p5gv-5qgc · GitHub severity CRITICAL · GitHub CVSS 9.8
  55. 2026-10-25 14:24 UTCEchelonGraph re-scored
  56. 2026-10-24 18:42 UTCEchelonGraph re-scored
  57. 2026-10-24 18:42 UTCVendor advisory
  58. 2026-10-24 18:42 UTCGHSA enrichmentGHSA-h6r3-p5gv-5qgc · GitHub severity CRITICAL · GitHub CVSS 9.8
  59. 2026-10-24 16:33 UTCEPSS rescoreEPSS 0.4% · 37th percentile
  60. 2026-10-23 20:55 UTCEchelonGraph re-scored
  61. 2026-10-23 20:55 UTCVendor advisory
  62. 2026-10-23 20:55 UTCGHSA enrichmentGHSA-h6r3-p5gv-5qgc · GitHub severity CRITICAL · GitHub CVSS 9.8
  63. 2026-10-23 16:32 UTCEPSS rescoreEPSS 0.4% · 37th percentile
  64. 2026-10-22 23:07 UTCEchelonGraph re-scored
  65. 2026-10-22 23:07 UTCVendor advisory
  66. 2026-10-22 23:07 UTCGHSA enrichmentGHSA-h6r3-p5gv-5qgc · GitHub severity CRITICAL · GitHub CVSS 9.8
  67. 2026-10-22 16:34 UTCEPSS rescoreEPSS 0.4% · 37th percentile
  68. 2026-10-22 01:19 UTCEchelonGraph re-scored
  69. 2026-10-22 01:19 UTCVendor advisory
  70. 2026-10-22 01:19 UTCGHSA enrichmentGHSA-h6r3-p5gv-5qgc · GitHub severity CRITICAL · GitHub CVSS 9.8
  71. 2026-10-21 16:33 UTCEPSS rescoreEPSS 0.4% · 37th percentile
  72. 2026-10-21 03:26 UTCEchelonGraph re-scored
  73. 2026-10-21 03:26 UTCVendor advisory
  74. 2026-10-21 03:26 UTCGHSA enrichmentGHSA-h6r3-p5gv-5qgc · GitHub severity CRITICAL · GitHub CVSS 9.8
  75. 2026-10-20 16:33 UTCEPSS rescoreEPSS 0.4% · 35th percentile

Frequently asked(5)

What is CVE-2026-4720?
CVE-2026-4720 is a critical-severity vulnerability; its CVE record was published on March 24, 2026. Memory safety bugs present in Firefox ESR 140.8, Thunderbird ESR 140.8, Firefox 148 and Thunderbird 148. 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…
When was the CVE record for CVE-2026-4720 published?
The CVE record for CVE-2026-4720 was published on March 24, 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 July 15, 2026; the record at its source may have been updated since.
Is CVE-2026-4720 actively exploited?
CVE-2026-4720 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.4% probability of exploitation in the next 30 days (39th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-4720?
CVE-2026-4720 has a CVSS v3.1 base score of 9.8 (CISA-ADP / Vulnrichment enrichment; NVD's own analysis pending).
How do I remediate CVE-2026-4720?
A fix for CVE-2026-4720 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2026-4720 are linked in the Vendor Advisories panel on this page.

Dependency Blast Radius

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