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
Trending — 4 sources updated this week

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
38th
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 2026-11-01). 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_22026-04-15redhat
redhatthunderbird-0:140.9.0-1.el8_82026-04-15redhat
redhatthunderbird-0:140.9.0-1.el9_02026-04-15redhat
redhatthunderbird-0:140.9.0-1.el9_42026-04-15redhat
redhatthunderbird-0:140.9.0-1.el10_02026-04-15redhat
redhatthunderbird-0:140.9.0-1.el9_62026-04-15redhat
redhatthunderbird-0:140.9.0-1.el8_22026-04-15redhat
redhatfirefox-0:140.9.0-1.el9_22026-04-13redhat
redhatfirefox-0:140.9.0-1.el9_42026-04-13redhat
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.el8_82026-04-13redhat
redhatfirefox-0:140.9.0-1.el9_62026-04-13redhat
redhatfirefox-0:140.9.0-1.el8_42026-04-13redhat
redhatfirefox-0:140.9.0-1.el8_22026-04-13redhat
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.el10_12026-03-26redhat
redhatfirefox-0:140.9.0-1.el9_72026-03-26redhat
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 27× in last 7d / 101× 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 360 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 260 oldest rows on record are not shown and were not checked, so the counts can still include repeats.

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

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