CVE-2026-84138

MEDIUMNVD 6.56.5
EchelonGraph scoreMEDIUM confidence

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

Score 6.5 from GitHub Security Advisory published 2026-09-01. NVD baseline CVSS 6.5; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: EPSS, GitHub Security Advisory, NVD CVSS v3
Trending — 3 sources updated this week
6.5EG
EchelonGraph verdictMonitorRemediate within your standard update timelines at low or medium mission impact and sooner than that at high (the SSVC decision on this page).
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0.4%CVSS: 6.5Exploit: None knownExposed services: Not assessed

The CVE record names the fixed release — apply it.

Denial-of-service in the PDF Viewer component. This vulnerability was fixed in Firefox 155 and Thunderbird 155.

CVSS v3
6.5
EG Score
6.5MEDIUMmedium confidence
EG Risk
44
EG Risk 44/100

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed (value × EchelonGraph’s weight)
Severity65% × 45%
The EG Score, 6.5 of 10.
Exploitation0.4% × 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 partial (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: The CVE record names the fixed release. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.
EPSS PROB
0.4%
EPSS %ILE
29th
KEV
Not listed

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

The CVE record names the fixed release. 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 partial (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; 60 days if it is not.

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

September 1, 2026

Last Modified

September 3, 2026

Advisory Details (3)

Auto-updated Sep 3, 2026
Fix named in the CVE record.
Web page

Security Vulnerabilities fixed in Thunderbird 155 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2026-86/
Web page

Security Vulnerabilities fixed in Firefox 155 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2026-82/
Web page

Access Denied

https://bugzilla.mozilla.org/show_bug.cgi?id=2056164

Vendor Advisories for CVE-2026-84138(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 19× in last 7d / 85× 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 98 of 124 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. 2 repeat rows among the latest 100 are merged into the row they repeat. The 26 oldest rows on record are not shown and were not checked, so the counts can still include repeats.

  1. 2026-10-12 16:35 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  2. 2026-10-12 14:54 UTCEG score recompute
  3. 2026-10-11 19:18 UTCEG score recompute
  4. 2026-10-11 16:35 UTCEG score recompute
  5. 2026-10-11 13:52 UTCEG score recompute
  6. 2026-10-11 13:49 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  7. 2026-10-10 20:00 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  8. 2026-10-10 00:19 UTCEG score recompute
  9. 2026-10-10 00:19 UTCGHSA enrichmentGHSA-qgw4-jqw6-383q · GitHub CVSS 6.5
  10. 2026-10-09 20:07 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  11. 2026-10-09 02:09 UTCEG score recompute
  12. 2026-10-09 02:09 UTCGHSA enrichmentGHSA-qgw4-jqw6-383q · GitHub CVSS 6.5
  13. 2026-10-08 17:13 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  14. 2026-10-08 00:17 UTCEG score recompute
  15. 2026-10-08 00:17 UTCGHSA enrichmentGHSA-qgw4-jqw6-383q · GitHub CVSS 6.5
  16. 2026-10-07 23:48 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  17. 2026-10-06 18:51 UTCEG score recompute
  18. 2026-10-06 18:51 UTCGHSA enrichmentGHSA-qgw4-jqw6-383q · GitHub CVSS 6.5
  19. 2026-10-06 15:18 UTCEPSS rescoreEPSS 0.4% · 28th percentile
  20. 2026-10-05 21:01 UTCEG score recompute
  21. 2026-10-05 21:01 UTCGHSA enrichmentGHSA-qgw4-jqw6-383q · GitHub CVSS 6.5
  22. 2026-10-05 17:43 UTCEPSS rescoreEPSS 0.4% · 28th percentile
  23. 2026-10-04 23:22 UTCEPSS rescoreEPSS 0.4% · 28th percentile
  24. 2026-10-04 23:10 UTCGHSA enrichmentGHSA-qgw4-jqw6-383q · GitHub CVSS 6.5
  25. 2026-10-04 01:11 UTCEG score recompute
Show 73 more
  1. 2026-10-04 01:11 UTCGHSA enrichmentGHSA-qgw4-jqw6-383q · GitHub CVSS 6.5
  2. 2026-10-03 14:26 UTCEPSS rescoreEPSS 0.4% · 28th percentile
  3. 2026-10-03 01:31 UTCEG score recompute
  4. 2026-10-03 01:31 UTCGHSA enrichmentGHSA-qgw4-jqw6-383q · GitHub CVSS 6.5
  5. 2026-10-02 17:57 UTCEPSS rescoreEPSS 0.4% · 28th percentile
  6. 2026-10-02 03:38 UTCEG score recompute
  7. 2026-10-02 03:38 UTCGHSA enrichmentGHSA-qgw4-jqw6-383q · GitHub CVSS 6.5
  8. 2026-10-01 19:50 UTCEPSS rescoreEPSS 0.4% · 28th percentile
  9. 2026-10-01 05:15 UTCEG score recompute
  10. 2026-10-01 05:15 UTCGHSA enrichmentGHSA-qgw4-jqw6-383q · GitHub CVSS 6.5
  11. 2026-09-30 15:04 UTCEPSS rescoreEPSS 0.4% · 28th percentile
  12. 2026-09-30 07:22 UTCEG score recompute
  13. 2026-09-30 07:22 UTCGHSA enrichmentGHSA-qgw4-jqw6-383q · GitHub CVSS 6.5
  14. 2026-09-29 09:31 UTCEG score recompute
  15. 2026-09-29 09:31 UTCGHSA enrichmentGHSA-qgw4-jqw6-383q · GitHub CVSS 6.5
  16. 2026-09-28 13:52 UTCEPSS rescoreEPSS 0.4% · 28th percentile
  17. 2026-09-28 11:15 UTCEG score recompute
  18. 2026-09-28 11:15 UTCGHSA enrichmentGHSA-qgw4-jqw6-383q · GitHub CVSS 6.5
  19. 2026-09-27 13:48 UTCEPSS rescoreEPSS 0.4% · 28th percentile
  20. 2026-09-27 13:24 UTCEG score recompute
  21. 2026-09-27 13:24 UTCGHSA enrichmentGHSA-qgw4-jqw6-383q · GitHub CVSS 6.5
  22. 2026-09-26 15:59 UTCEPSS rescoreEPSS 0.4% · 28th percentile
  23. 2026-09-26 15:32 UTCEG score recompute
  24. 2026-09-26 15:32 UTCGHSA enrichmentGHSA-qgw4-jqw6-383q · GitHub CVSS 6.5
  25. 2026-09-25 16:31 UTCGHSA enrichmentGHSA-qgw4-jqw6-383q · GitHub CVSS 6.5
  26. 2026-09-24 18:33 UTCEG score recompute
  27. 2026-09-24 18:33 UTCGHSA enrichmentGHSA-qgw4-jqw6-383q · GitHub CVSS 6.5
  28. 2026-09-24 14:04 UTCEPSS rescoreEPSS 0.4% · 28th percentile
  29. 2026-09-23 19:50 UTCEG score recompute
  30. 2026-09-23 19:50 UTCGHSA enrichmentGHSA-qgw4-jqw6-383q · GitHub CVSS 6.5
  31. 2026-09-23 17:54 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  32. 2026-09-22 21:57 UTCEG score recompute
  33. 2026-09-22 21:57 UTCGHSA enrichmentGHSA-qgw4-jqw6-383q · GitHub CVSS 6.5
  34. 2026-09-22 16:01 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  35. 2026-09-22 00:06 UTCEG score recompute
  36. 2026-09-22 00:06 UTCGHSA enrichmentGHSA-qgw4-jqw6-383q · GitHub CVSS 6.5
  37. 2026-09-21 21:09 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  38. 2026-09-21 02:14 UTCEG score recompute
  39. 2026-09-21 02:14 UTCGHSA enrichmentGHSA-qgw4-jqw6-383q · GitHub CVSS 6.5
  40. 2026-09-20 20:16 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  41. 2026-09-20 04:23 UTCEG score recompute
  42. 2026-09-20 04:23 UTCGHSA enrichmentGHSA-qgw4-jqw6-383q · GitHub CVSS 6.5
  43. 2026-09-19 06:32 UTCEG score recompute
  44. 2026-09-19 06:31 UTCGHSA enrichmentGHSA-qgw4-jqw6-383q · GitHub CVSS 6.5
  45. 2026-09-18 19:28 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  46. 2026-09-18 08:40 UTCEG score recompute
  47. 2026-09-18 08:40 UTCGHSA enrichmentGHSA-qgw4-jqw6-383q · GitHub CVSS 6.5
  48. 2026-09-17 19:32 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  49. 2026-09-17 10:49 UTCEG score recompute
  50. 2026-09-17 10:49 UTCGHSA enrichmentGHSA-qgw4-jqw6-383q · GitHub CVSS 6.5
  51. 2026-09-16 14:09 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  52. 2026-09-16 12:58 UTCEG score recompute
  53. 2026-09-16 12:57 UTCGHSA enrichmentGHSA-qgw4-jqw6-383q · GitHub CVSS 6.5
  54. 2026-09-16 05:15 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  55. 2026-09-15 15:06 UTCEG score recompute
  56. 2026-09-15 15:06 UTCGHSA enrichmentGHSA-qgw4-jqw6-383q · GitHub CVSS 6.5
  57. 2026-09-15 03:12 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  58. 2026-09-14 17:06 UTCGHSA enrichmentGHSA-qgw4-jqw6-383q · GitHub CVSS 6.5
  59. 2026-09-13 19:15 UTCEG score recompute
  60. 2026-09-13 19:15 UTCGHSA enrichmentGHSA-qgw4-jqw6-383q · GitHub CVSS 6.5
  61. 2026-09-12 21:24 UTCEG score recompute
  62. 2026-09-12 21:24 UTCGHSA enrichmentGHSA-qgw4-jqw6-383q · GitHub CVSS 6.5
  63. 2026-09-11 23:33 UTCEG score recompute
  64. 2026-09-11 23:33 UTCGHSA enrichmentGHSA-qgw4-jqw6-383q · GitHub CVSS 6.5
  65. 2026-09-11 14:53 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  66. 2026-09-11 01:42 UTCEG score recompute
  67. 2026-09-11 01:42 UTCGHSA enrichmentGHSA-qgw4-jqw6-383q · GitHub CVSS 6.5
  68. 2026-09-10 03:50 UTCGHSA enrichmentGHSA-qgw4-jqw6-383q · GitHub CVSS 6.5
  69. 2026-09-09 05:59 UTCEG score recompute
  70. 2026-09-09 05:59 UTCGHSA enrichmentGHSA-qgw4-jqw6-383q · GitHub CVSS 6.5
  71. 2026-09-08 22:01 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  72. 2026-09-08 08:08 UTCEG score recompute
  73. 2026-09-08 08:08 UTCGHSA enrichmentGHSA-qgw4-jqw6-383q · GitHub CVSS 6.5

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Frequently asked(5)

What is CVE-2026-84138?
CVE-2026-84138 is a medium-severity vulnerability; its CVE record was published on September 1, 2026. Denial-of-service in the PDF Viewer component. This vulnerability was fixed in Firefox 155 and Thunderbird 155.
When was the CVE record for CVE-2026-84138 published?
The CVE record for CVE-2026-84138 was published on September 1, 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 September 3, 2026; the record at its source may have been updated since.
Is CVE-2026-84138 actively exploited?
CVE-2026-84138 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.4% probability of exploitation in the next 30 days (29th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-84138?
CVE-2026-84138 has a CVSS v3 base score of 6.5 (NVD).
How do I remediate CVE-2026-84138?
The CVE record for CVE-2026-84138 names the fix: "This vulnerability was fixed in Firefox 155 and Thunderbird 155." The vendor advisories EchelonGraph has for CVE-2026-84138 are linked in the Vendor Advisories panel on this page.

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