CVE-2026-16375

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 2026-07-21. 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-2026-46211 (ENISA EUVD) · GHSA-fg69-c79m-xpwv (GitHub Security Advisories)Source: ENISA EUVD

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: 0.3%CVSS: 9.8Exploit: None knownExposed services: Not assessed

A fix is available — apply it.

Site isolation issue in the Networking: HTTP component. This vulnerability was fixed in Firefox 153, Firefox ESR 140.13, Thunderbird 153, and Thunderbird 140.13.

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.
Exploitation0.3% × 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
0.3%
EPSS %ILE
21st
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 2026-10-26). 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

July 21, 2026

Last Modified

October 24, 2026

Advisory Details (5)

Auto-updated Oct 26, 2026
Patch available.
Web page

Security Vulnerabilities fixed in Thunderbird 140.13 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2026-72/
Web page

Security Vulnerabilities fixed in Thunderbird 153 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2026-71/
Web page

Security Vulnerabilities fixed in Firefox ESR 140.13 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2026-70/
Web page

Security Vulnerabilities fixed in Firefox 153 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2026-68/
Web page

2032140 - (CVE-2026-16375) BackgroundChannelRegistrar does not isolate by ContentParentId — any renderer can hijack the HttpBackgroundChannel of another process and receive its HTTP response data

https://bugzilla.mozilla.org/show_bug.cgi?id=2032140

Patch Availability(21)

Vendor / EcosystemFix (by version range) / PatchReleasedSource
redhatfirefox-0:140.13.0-1.el8_82026-08-12redhat
redhatfirefox-0:140.13.0-1.el9_22026-08-12redhat
redhatfirefox-0:140.13.0-1.el10_02026-08-12redhat
redhatfirefox-0:140.13.0-1.el8_42026-08-12redhat
redhatfirefox-0:140.13.0-1.el9_42026-08-12redhat
redhatfirefox-0:140.13.0-1.el9_62026-08-12redhat
redhatfirefox-0:140.13.0-1.el7_92026-08-12redhat
redhatfirefox-0:140.13.0-1.el8_62026-08-12redhat
redhatthunderbird-0:140.13.0-1.el10_02026-08-11redhat
redhatthunderbird-0:140.13.0-1.el9_42026-08-11redhat
redhatthunderbird-0:140.13.0-1.el9_22026-08-11redhat
redhatthunderbird-0:140.13.0-1.el8_42026-08-11redhat
redhatthunderbird-0:140.13.0-1.el9_62026-08-11redhat
redhatthunderbird-0:140.13.0-1.el8_62026-08-11redhat
redhatthunderbird-0:140.13.0-1.el8_82026-08-11redhat
redhatthunderbird-0:140.13.0-1.el9_82026-08-04redhat
redhatthunderbird-0:140.13.0-1.el8_102026-08-04redhat
redhatfirefox-0:140.13.0-1.el9_82026-08-03redhat
redhatthunderbird-0:140.13.0-1.el10_22026-08-03redhat
redhatfirefox-0:140.13.0-1.el10_22026-07-28redhat
redhatfirefox-0:140.13.0-1.el8_102026-07-28redhat

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 (283 versions)
  • every version up to 140.13.0esr-1~deb11u1: fixed in 140.13.0esr-1~deb11u1
—
thunderbird1:102.0.1-1 ... 1:91.9.0-1~deb9u1 (334 versions)
  • every version up to 1:140.13.0esr-1: fixed in 1:140.13.0esr-1
—
Debian:12(2)
PackageVulnerable rangeFix by version rangeDependents
firefox-esr102.11.0esr-1 ... 140.9.1esr-1~deb13u1 (190 versions)
  • every version up to 140.13.0esr-1~deb12u1: fixed in 140.13.0esr-1~deb12u1
—
thunderbird1:102.11.0-1 ... 1:140.9.1esr-1~deb13u1 (220 versions)
  • every version up to 1:140.13.0esr-2~deb12u1: fixed in 1:140.13.0esr-2~deb12u1
—
Debian:13(2)
PackageVulnerable rangeFix by version rangeDependents
firefox-esr128.13.0esr-1 ... 140.9.1esr-1~deb13u1 (66 versions)
  • every version up to 140.13.0esr-1~deb13u1: fixed in 140.13.0esr-1~deb13u1
—
thunderbird1:128.13.0esr-1 ... 1:140.9.1esr-1~deb13u1 (76 versions)
  • every version up to 1:140.13.0esr-2~deb13u1: fixed in 1:140.13.0esr-2~deb13u1
—
Debian:14(2)
PackageVulnerable rangeFix by version rangeDependents
firefox-esr128.13.0esr-1 ... 140.9.1esr-1~deb13u1 (67 versions)
  • every version up to 140.13.0esr-1: fixed in 140.13.0esr-1
—
thunderbird1:128.13.0esr-1 ... 1:140.9.1esr-1~deb13u1 (73 versions)
  • every version up to 1:140.13.0esr-1: fixed in 1:140.13.0esr-1
—

Weakness Classification(1)

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

Additional Vendor Advisories

(1)

Vendors that published advisories for this CVE beyond the curated set above. Broader coverage but minimal per-row detail — click through for the original advisory.

Data Freshness Timeline

(refreshed 29× in last 7d / 94× 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 662 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 562 oldest rows on record are not shown and were not checked, so the counts can still include repeats.

  1. 2026-10-27 16:31 UTCEPSS rescoreEPSS 0.3% · 21st percentile
  2. 2026-10-27 03:01 UTCEG score recompute
  3. 2026-10-27 03:01 UTCVendor advisory
  4. 2026-10-27 03:01 UTCGHSA enrichmentGHSA-fg69-c79m-xpwv · GitHub severity CRITICAL · GitHub CVSS 9.8
  5. 2026-10-26 16:31 UTCEPSS rescoreEPSS 0.3% · 21st percentile
  6. 2026-10-25 21:46 UTCEG score recompute
  7. 2026-10-25 21:46 UTCVendor advisory
  8. 2026-10-25 21:46 UTCGHSA enrichmentGHSA-fg69-c79m-xpwv · GitHub severity CRITICAL · GitHub CVSS 9.8
  9. 2026-10-25 16:32 UTCEPSS rescoreEPSS 0.3% · 21st percentile
  10. 2026-10-25 14:46 UTCEG score recompute
  11. 2026-10-24 20:26 UTCEG score recompute
  12. 2026-10-24 20:26 UTCVendor advisory
  13. 2026-10-24 20:26 UTCGHSA enrichmentGHSA-fg69-c79m-xpwv · GitHub severity CRITICAL · GitHub CVSS 9.8
  14. 2026-10-24 16:32 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  15. 2026-10-24 05:53 UTCEG score recompute
  16. 2026-10-24 05:53 UTCVendor advisory
  17. 2026-10-24 05:53 UTCGHSA enrichmentGHSA-fg69-c79m-xpwv · GitHub severity CRITICAL · GitHub CVSS 9.8
  18. 2026-10-23 16:31 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  19. 2026-10-23 04:38 UTCEG score recompute
  20. 2026-10-23 04:38 UTCVendor advisory
  21. 2026-10-23 04:37 UTCGHSA enrichmentGHSA-fg69-c79m-xpwv · GitHub severity CRITICAL · GitHub CVSS 9.8
  22. 2026-10-22 16:33 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  23. 2026-10-22 03:25 UTCEG score recompute
  24. 2026-10-22 03:25 UTCVendor advisory
  25. 2026-10-22 03:25 UTCGHSA enrichmentGHSA-fg69-c79m-xpwv · GitHub severity CRITICAL · GitHub CVSS 9.8
Show 75 more
  1. 2026-10-21 16:32 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  2. 2026-10-21 02:12 UTCEG score recompute
  3. 2026-10-21 02:12 UTCVendor advisory
  4. 2026-10-21 02:12 UTCGHSA enrichmentGHSA-fg69-c79m-xpwv · GitHub severity CRITICAL · GitHub CVSS 9.8
  5. 2026-10-20 16:32 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  6. 2026-10-20 00:58 UTCEG score recompute
  7. 2026-10-20 00:58 UTCVendor advisory
  8. 2026-10-20 00:58 UTCGHSA enrichmentGHSA-fg69-c79m-xpwv · GitHub severity CRITICAL · GitHub CVSS 9.8
  9. 2026-10-19 16:31 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  10. 2026-10-18 23:44 UTCEG score recompute
  11. 2026-10-18 23:44 UTCVendor advisory
  12. 2026-10-18 23:43 UTCGHSA enrichmentGHSA-fg69-c79m-xpwv · GitHub severity CRITICAL · GitHub CVSS 9.8
  13. 2026-10-18 16:31 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  14. 2026-10-18 04:00 UTCEG score recompute
  15. 2026-10-17 22:31 UTCEG score recompute
  16. 2026-10-17 22:31 UTCVendor advisory
  17. 2026-10-17 22:31 UTCGHSA enrichmentGHSA-fg69-c79m-xpwv · GitHub severity CRITICAL · GitHub CVSS 9.8
  18. 2026-10-17 16:33 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  19. 2026-10-16 21:19 UTCEG score recompute
  20. 2026-10-16 21:19 UTCVendor advisory
  21. 2026-10-16 21:19 UTCGHSA enrichmentGHSA-fg69-c79m-xpwv · GitHub severity CRITICAL · GitHub CVSS 9.8
  22. 2026-10-16 16:40 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  23. 2026-10-15 18:15 UTCEG score recompute
  24. 2026-10-15 18:15 UTCVendor advisory
  25. 2026-10-15 18:14 UTCGHSA enrichmentGHSA-fg69-c79m-xpwv · GitHub severity CRITICAL · GitHub CVSS 9.8
  26. 2026-10-15 16:31 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  27. 2026-10-14 16:32 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  28. 2026-10-14 12:00 UTCEG score recompute
  29. 2026-10-14 12:00 UTCVendor advisory
  30. 2026-10-14 12:00 UTCGHSA enrichmentGHSA-fg69-c79m-xpwv · GitHub severity CRITICAL · GitHub CVSS 9.8
  31. 2026-10-13 16:33 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  32. 2026-10-13 10:48 UTCEG score recompute
  33. 2026-10-13 10:48 UTCVendor advisory
  34. 2026-10-13 10:47 UTCGHSA enrichmentGHSA-fg69-c79m-xpwv · GitHub severity CRITICAL · GitHub CVSS 9.8
  35. 2026-10-12 16:33 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  36. 2026-10-12 16:30 UTCEG score recompute
  37. 2026-10-12 09:36 UTCVendor advisory
  38. 2026-10-12 09:35 UTCGHSA enrichmentGHSA-fg69-c79m-xpwv · GitHub severity CRITICAL · GitHub CVSS 9.8
  39. 2026-10-11 20:09 UTCEG score recompute
  40. 2026-10-11 17:21 UTCEG score recompute
  41. 2026-10-11 14:54 UTCEG score recompute
  42. 2026-10-11 13:48 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  43. 2026-10-10 19:59 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  44. 2026-10-09 20:06 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  45. 2026-10-08 17:11 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  46. 2026-10-07 23:47 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  47. 2026-10-06 15:17 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  48. 2026-10-05 17:42 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  49. 2026-10-04 23:21 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  50. 2026-10-04 14:51 UTCEG score recompute
  51. 2026-10-04 14:51 UTCVendor advisory
  52. 2026-10-04 14:51 UTCGHSA enrichmentGHSA-fg69-c79m-xpwv · GitHub severity CRITICAL · GitHub CVSS 9.8
  53. 2026-10-03 14:25 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  54. 2026-10-01 19:49 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  55. 2026-10-01 15:53 UTCVendor advisory
  56. 2026-10-01 15:53 UTCGHSA enrichmentGHSA-fg69-c79m-xpwv · GitHub severity CRITICAL · GitHub CVSS 9.8
  57. 2026-10-01 11:33 UTCVendor advisory
  58. 2026-10-01 11:33 UTCGHSA enrichmentGHSA-fg69-c79m-xpwv · GitHub severity CRITICAL · GitHub CVSS 9.8
  59. 2026-10-01 07:33 UTCEG score recompute
  60. 2026-10-01 07:33 UTCVendor advisory
  61. 2026-10-01 07:33 UTCGHSA enrichmentGHSA-fg69-c79m-xpwv · GitHub severity CRITICAL · GitHub CVSS 9.8
  62. 2026-09-30 15:02 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  63. 2026-09-29 15:20 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  64. 2026-09-28 13:51 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  65. 2026-09-28 10:25 UTCVendor advisory
  66. 2026-09-28 10:25 UTCGHSA enrichmentGHSA-fg69-c79m-xpwv · GitHub severity CRITICAL · GitHub CVSS 9.8
  67. 2026-09-28 06:12 UTCEG score recompute
  68. 2026-09-28 06:12 UTCVendor advisory
  69. 2026-09-28 06:12 UTCGHSA enrichmentGHSA-fg69-c79m-xpwv · GitHub severity CRITICAL · GitHub CVSS 9.8
  70. 2026-09-27 13:47 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  71. 2026-09-26 15:58 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  72. 2026-09-24 13:09 UTCVendor advisory
  73. 2026-09-24 13:09 UTCGHSA enrichmentGHSA-fg69-c79m-xpwv · GitHub severity CRITICAL · GitHub CVSS 9.8
  74. 2026-09-24 08:19 UTCVendor advisory
  75. 2026-09-24 08:19 UTCGHSA enrichmentGHSA-fg69-c79m-xpwv · GitHub severity CRITICAL · GitHub CVSS 9.8

Frequently asked(5)

What is CVE-2026-16375?
CVE-2026-16375 is a critical-severity vulnerability; its CVE record was published on July 21, 2026. Site isolation issue in the Networking: HTTP component. This vulnerability was fixed in Firefox 153, Firefox ESR 140.13, Thunderbird 153, and Thunderbird 140.13.
When was the CVE record for CVE-2026-16375 published?
The CVE record for CVE-2026-16375 was published on July 21, 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-2026-16375 actively exploited?
CVE-2026-16375 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.3% probability of exploitation in the next 30 days (21st percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-16375?
CVE-2026-16375 has a CVSS v3.1 base score of 9.8 (CISA-ADP / Vulnrichment enrichment; NVD's own analysis pending).
How do I remediate CVE-2026-16375?
A fix for CVE-2026-16375 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2026-16375 are linked in the Vendor Advisories panel on this page.

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