CVE-2026-2777

CRITICALNVD 9.89.8
EchelonGraph scoreMEDIUM confidence

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

Score 9.8 from GitHub Security Advisory (severity: CRITICAL) published 2026-02-24. NVD baseline CVSS 9.8; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: EPSS, GitHub Security Advisory, NVD CVSS v3
Trending — 4 sources updated this week
9.8EG
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).
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0.7%CVSS: 9.8Exploit: None knownExposed services: Not assessed

A fix is available — apply it.

Privilege escalation in the Messaging System component. This vulnerability was fixed in Firefox 148, Firefox ESR 115.33, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8.

CVSS v3
9.8
EG Score
9.8CRITICALmedium confidence
EG Risk
59
EG Risk 59/100

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.
Exploitation0.7% × 40%
FIRST EPSS: the 30-day exploitation probability when EchelonGraph scored this CVE.
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 none (CISA Vulnrichment) · Automatable yes (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 at low or medium mission impact and sooner than that at high.
EPSS PROB
0.7%
EPSS %ILE
50th
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
0.7% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-10-23). 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; Attend at high (mission-essential systems).CISA BOD 26-04: 3 days if the affected system is publicly exposed; 60 days 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; 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 none (CISA Vulnrichment) · Automatable yes (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)3 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 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

February 24, 2026

Last Modified

July 15, 2026

Advisory Details (10)

Auto-updated Oct 18, 2026
Patch available. Sources: redhat.
Red HatMentions a patch (unverified)

Affected: Red Hat Enterprise Linux 8.4 Advanced Mission Critical Update Support and Red Hat Enterprise Linux 8.4 Extended Update Support

https://access.redhat.com/errata/RHSA-2026:3491
Red HatMentions a patch (unverified)

Affected: Red Hat Enterprise Linux 10.

https://access.redhat.com/errata/RHSA-2026:3361
Red HatMentions a patch (unverified)

Affected: Red Hat Enterprise Linux 9.

https://access.redhat.com/errata/RHSA-2026:3339
Red HatMentions a patch (unverified)

Affected: Red Hat Enterprise Linux 8.

https://access.redhat.com/errata/RHSA-2026:3338
Web page

Security Vulnerabilities fixed in Thunderbird 140.8 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2026-17/
Web page

Security Vulnerabilities fixed in Thunderbird 148 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2026-16/
Web page

Security Vulnerabilities fixed in Firefox ESR 140.8 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2026-15/
Web page

Security Vulnerabilities fixed in Firefox ESR 115.33 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2026-14/
Web page

Security Vulnerabilities fixed in Firefox 148 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2026-13/
Web page

2015305 - (CVE-2026-2777) Compromised content process installs arbitrary WebExtensions or homepage hijacks (1-click) via AboutMessagePreviewParent IPC

https://bugzilla.mozilla.org/show_bug.cgi?id=2015305

Patch Availability(25)

Vendor / EcosystemFix (by version range) / PatchReleasedSource
redhatthunderbird-0:140.8.0-1.el8_22026-03-12redhat
redhatthunderbird-0:140.8.0-2.el10_02026-03-11redhat
redhatfirefox-0:140.8.0-2.el9_22026-03-10redhat
redhatthunderbird-0:140.8.0-1.el9_62026-03-09redhat
redhatthunderbird-0:140.8.0-1.el9_02026-03-09redhat
redhatfirefox-0:140.8.0-2.el7_92026-03-09redhat
redhatthunderbird-0:140.8.0-1.el9_42026-03-09redhat
redhatthunderbird-0:140.8.0-1.el9_22026-03-09redhat
redhatfirefox-0:140.8.0-2.el10_02026-03-09redhat
redhatthunderbird-0:140.8.0-1.el8_82026-03-09redhat
redhatthunderbird-0:140.8.0-2.el8_42026-03-09redhat
redhatthunderbird-0:140.8.0-1.el8_62026-03-09redhat
redhatthunderbird-0:140.8.0-1.el8_102026-03-02redhat
redhatfirefox-0:140.8.0-2.el8_62026-03-02redhat
redhatfirefox-0:140.8.0-2.el8_22026-03-02redhat
redhatfirefox-0:140.8.0-2.el8_42026-03-02redhat
redhatthunderbird-0:140.8.0-2.el10_12026-03-02redhat
redhatthunderbird-0:140.8.0-1.el9_72026-03-02redhat
redhatfirefox-0:140.8.0-2.el9_62026-03-02redhat
redhatfirefox-0:140.8.0-2.el8_82026-03-02redhat
redhatfirefox-0:140.8.0-2.el9_02026-03-02redhat
redhatfirefox-0:140.8.0-2.el9_42026-03-02redhat
redhatfirefox-0:140.8.0-2.el8_102026-02-25redhat
redhatfirefox-0:140.8.0-2.el9_72026-02-25redhat
redhatfirefox-0:140.8.0-2.el10_12026-02-25redhat

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 (251 versions)
  • every version up to 140.8.0esr-1~deb11u1: fixed in 140.8.0esr-1~deb11u1
—
thunderbird1:102.0.1-1 ... 1:91.9.0-1~deb9u1 (302 versions)
  • every version up to 1:140.8.0esr-1~deb11u1: fixed in 1:140.8.0esr-1~deb11u1
—
Debian:12(2)
PackageVulnerable rangeFix by version rangeDependents
firefox-esr102.11.0esr-1 ... 140.8.0esr-1~deb11u1 (158 versions)
  • every version up to 140.8.0esr-1~deb12u1: fixed in 140.8.0esr-1~deb12u1
—
thunderbird1:102.11.0-1 ... 1:140.8.0esr-1~deb11u1 (187 versions)
  • every version up to 1:140.8.0esr-1~deb12u1: fixed in 1:140.8.0esr-1~deb12u1
—
Debian:13(2)
PackageVulnerable rangeFix by version rangeDependents
firefox-esr128.13.0esr-1 ... 140.8.0esr-1~deb12u1 (34 versions)
  • every version up to 140.8.0esr-1~deb13u1: fixed in 140.8.0esr-1~deb13u1
—
thunderbird1:128.13.0esr-1 ... 1:140.8.0esr-1~deb12u1 (43 versions)
  • every version up to 1:140.8.0esr-1~deb13u1: fixed in 1:140.8.0esr-1~deb13u1
—
Debian:14(2)
PackageVulnerable rangeFix by version rangeDependents
firefox-esr128.13.0esr-1 ... 140.8.0esr-1~deb13u1 (35 versions)
  • every version up to 140.8.0esr-1: fixed in 140.8.0esr-1
—
thunderbird1:128.13.0esr-1 ... 1:140.8.0esr-1~deb13u1 (44 versions)
  • every version up to 1:140.8.0esr-1: fixed in 1:140.8.0esr-1
—

Weakness Classification(1)

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

Additional Vendor Advisories

(5)

Data Freshness Timeline

(refreshed 29× in last 7d / 67× 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 95 of 311 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. 5 repeat rows among the latest 100 are merged into the row they repeat. The 216 oldest rows on record are not shown and were not checked, so the counts can still include repeats.

  1. 2026-10-23 17:45 UTCEG score recompute
  2. 2026-10-23 17:45 UTCVendor advisory
  3. 2026-10-23 17:45 UTCGHSA enrichmentGHSA-hjq8-wc3q-9xf3 · GitHub severity CRITICAL · GitHub CVSS 9.8
  4. 2026-10-23 16:31 UTCEPSS rescoreEPSS 0.7% · 50th percentile
  5. 2026-10-22 18:00 UTCEG score recompute
  6. 2026-10-22 18:00 UTCVendor advisory
  7. 2026-10-22 18:00 UTCGHSA enrichmentGHSA-hjq8-wc3q-9xf3 · GitHub severity CRITICAL · GitHub CVSS 9.8
  8. 2026-10-22 16:34 UTCEPSS rescoreEPSS 0.7% · 50th percentile
  9. 2026-10-21 17:44 UTCEG score recompute
  10. 2026-10-21 17:44 UTCVendor advisory
  11. 2026-10-21 17:44 UTCGHSA enrichmentGHSA-hjq8-wc3q-9xf3 · GitHub severity CRITICAL · GitHub CVSS 9.8
  12. 2026-10-21 16:32 UTCEPSS rescoreEPSS 0.6% · 46th percentile
  13. 2026-10-20 18:00 UTCEG score recompute
  14. 2026-10-20 18:00 UTCVendor advisory
  15. 2026-10-20 17:59 UTCGHSA enrichmentGHSA-hjq8-wc3q-9xf3 · GitHub severity CRITICAL · GitHub CVSS 9.8
  16. 2026-10-20 16:32 UTCEPSS rescoreEPSS 0.6% · 46th percentile
  17. 2026-10-19 18:13 UTCEG score recompute
  18. 2026-10-19 18:13 UTCVendor advisory
  19. 2026-10-19 18:12 UTCGHSA enrichmentGHSA-hjq8-wc3q-9xf3 · GitHub severity CRITICAL · GitHub CVSS 9.8
  20. 2026-10-19 16:31 UTCEPSS rescoreEPSS 0.6% · 46th percentile
  21. 2026-10-18 18:25 UTCEG score recompute
  22. 2026-10-18 18:25 UTCVendor advisory
  23. 2026-10-18 18:25 UTCGHSA enrichmentGHSA-hjq8-wc3q-9xf3 · GitHub severity CRITICAL · GitHub CVSS 9.8
  24. 2026-10-18 16:31 UTCEPSS rescoreEPSS 0.6% · 46th percentile
  25. 2026-10-18 03:51 UTCEG score recompute
Show 70 more
  1. 2026-10-17 18:39 UTCEG score recompute
  2. 2026-10-17 18:39 UTCVendor advisory
  3. 2026-10-17 18:39 UTCGHSA enrichmentGHSA-hjq8-wc3q-9xf3 · GitHub severity CRITICAL · GitHub CVSS 9.8
  4. 2026-10-17 16:33 UTCEPSS rescoreEPSS 0.6% · 46th percentile
  5. 2026-10-16 18:53 UTCEG score recompute
  6. 2026-10-16 18:53 UTCVendor advisory
  7. 2026-10-16 18:53 UTCGHSA enrichmentGHSA-hjq8-wc3q-9xf3 · GitHub severity CRITICAL · GitHub CVSS 9.8
  8. 2026-10-16 16:41 UTCEPSS rescoreEPSS 0.6% · 46th percentile
  9. 2026-10-15 16:31 UTCEPSS rescoreEPSS 0.6% · 46th percentile
  10. 2026-10-15 16:03 UTCEG score recompute
  11. 2026-10-15 16:03 UTCVendor advisory
  12. 2026-10-15 16:03 UTCGHSA enrichmentGHSA-hjq8-wc3q-9xf3 · GitHub severity CRITICAL · GitHub CVSS 9.8
  13. 2026-10-14 16:32 UTCEPSS rescoreEPSS 0.6% · 46th percentile
  14. 2026-10-14 10:13 UTCEG score recompute
  15. 2026-10-14 10:13 UTCVendor advisory
  16. 2026-10-14 10:13 UTCGHSA enrichmentGHSA-hjq8-wc3q-9xf3 · GitHub severity CRITICAL · GitHub CVSS 9.8
  17. 2026-10-13 16:34 UTCEPSS rescoreEPSS 0.6% · 46th percentile
  18. 2026-10-13 08:37 UTCEG score recompute
  19. 2026-10-13 08:37 UTCVendor advisory
  20. 2026-10-13 08:36 UTCGHSA enrichmentGHSA-hjq8-wc3q-9xf3 · GitHub severity CRITICAL · GitHub CVSS 9.8
  21. 2026-10-12 16:34 UTCEPSS rescoreEPSS 0.6% · 45th percentile
  22. 2026-10-12 16:17 UTCEG score recompute
  23. 2026-10-12 08:50 UTCVendor advisory
  24. 2026-10-12 08:49 UTCGHSA enrichmentGHSA-hjq8-wc3q-9xf3 · GitHub severity CRITICAL · GitHub CVSS 9.8
  25. 2026-10-11 19:59 UTCEG score recompute
  26. 2026-10-11 17:13 UTCEG score recompute
  27. 2026-10-11 14:44 UTCEG score recompute
  28. 2026-10-11 13:48 UTCEPSS rescoreEPSS 0.6% · 45th percentile
  29. 2026-10-10 20:00 UTCEPSS rescoreEPSS 0.6% · 45th percentile
  30. 2026-10-09 20:07 UTCEPSS rescoreEPSS 0.6% · 45th percentile
  31. 2026-10-09 14:58 UTCOSV refresh
  32. 2026-10-08 17:12 UTCEPSS rescoreEPSS 0.6% · 45th percentile
  33. 2026-10-07 23:47 UTCEPSS rescoreEPSS 0.6% · 45th percentile
  34. 2026-10-06 15:17 UTCEPSS rescoreEPSS 0.6% · 45th percentile
  35. 2026-10-05 17:42 UTCEPSS rescoreEPSS 0.6% · 45th percentile
  36. 2026-10-04 23:21 UTCEPSS rescoreEPSS 0.6% · 45th percentile
  37. 2026-10-03 14:25 UTCEPSS rescoreEPSS 0.6% · 45th percentile
  38. 2026-10-01 19:49 UTCEPSS rescoreEPSS 0.6% · 45th percentile
  39. 2026-09-30 15:03 UTCEPSS rescoreEPSS 0.6% · 44th percentile
  40. 2026-09-28 13:51 UTCEPSS rescoreEPSS 0.6% · 44th percentile
  41. 2026-09-26 15:58 UTCEPSS rescoreEPSS 0.6% · 44th percentile
  42. 2026-09-26 00:26 UTCEPSS rescoreEPSS 0.6% · 44th percentile
  43. 2026-09-20 20:15 UTCEPSS rescoreEPSS 0.4% · 30th percentile
  44. 2026-09-19 22:21 UTCOSV refresh
  45. 2026-09-18 19:27 UTCEPSS rescoreEPSS 0.4% · 30th percentile
  46. 2026-09-17 19:30 UTCEPSS rescoreEPSS 0.4% · 30th percentile
  47. 2026-09-16 14:08 UTCEPSS rescoreEPSS 0.4% · 30th percentile
  48. 2026-09-16 05:15 UTCEPSS rescoreEPSS 0.4% · 30th percentile
  49. 2026-09-13 16:47 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  50. 2026-09-12 15:01 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  51. 2026-09-11 14:52 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  52. 2026-09-10 09:34 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  53. 2026-09-08 22:00 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  54. 2026-09-07 16:01 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  55. 2026-09-06 13:47 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  56. 2026-09-04 05:06 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  57. 2026-09-02 14:11 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  58. 2026-09-01 13:53 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  59. 2026-09-01 04:39 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  60. 2026-09-01 02:04 UTCOSV refresh
  61. 2026-08-30 19:17 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  62. 2026-08-30 01:22 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  63. 2026-08-28 21:41 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  64. 2026-08-27 14:25 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  65. 2026-08-26 14:46 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  66. 2026-08-25 13:49 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  67. 2026-08-24 14:17 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  68. 2026-08-23 00:19 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  69. 2026-08-21 23:49 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  70. 2026-08-20 22:55 UTCEPSS rescoreEPSS 0.4% · 29th percentile

Frequently asked(5)

What is CVE-2026-2777?
CVE-2026-2777 is a critical-severity vulnerability; its CVE record was published on February 24, 2026. Privilege escalation in the Messaging System component. This vulnerability was fixed in Firefox 148, Firefox ESR 115.33, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8.
When was the CVE record for CVE-2026-2777 published?
The CVE record for CVE-2026-2777 was published on February 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-2026-2777 actively exploited?
CVE-2026-2777 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.7% probability of exploitation in the next 30 days (50th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-2777?
CVE-2026-2777 has a CVSS v3 base score of 9.8 (NVD).
How do I remediate CVE-2026-2777?
A fix for CVE-2026-2777 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2026-2777 are linked in the Vendor Advisories panel on this page.

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