CVE-2020-26958

MEDIUMNVD 6.16.1—
EchelonGraph scoreMEDIUM confidence

This medium-severity CVE scores 6.1 under NVD CVSS v3. EPSS exploit probability: 1.3%, top 32% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, nvd
6.1EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 1%CVSS: 6.1Exploit: None knownExposed: 0

A fix is available — apply it.

Firefox did not block execution of scripts with incorrect MIME types when the response was intercepted and cached through a ServiceWorker. This could lead to a cross-site script inclusion vulnerability, or a Content Security Policy bypass. This vulnerability affects Firefox < 83, Firefox ESR < 78.5, and Thunderbird < 78.5.

CVSS v3
6.1
EG Score
6.1(medium)
EG Risk
32(Track)
EG Risk 32/100SSVC: Track

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
Severity61% × 45%
Exploitation1% × 40%
Automatability30% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
1%
EPSS %ILE
68%
KEV
Not listed

Published

December 9, 2020

Last Modified

November 21, 2024

References (8)

Patch Availability(15)

Vendor / EcosystemFixed in / PatchReleasedSource
ubuntufirefox-mozsymbols (83.0+build2-0ubuntu0.18.04.2) @ bionic2026-05-23ubuntu
ubuntufirefox-mozsymbols (83.0+build2-0ubuntu0.16.04.3) @ xenial2026-05-23ubuntu
ubuntuxul-ext-lightning (1:78.5.0+build3-0ubuntu0.20.10.1) @ groovy2026-05-23ubuntu
redhatfirefox-0:78.5.0-1.el8_02020-12-01redhat
redhatfirefox-0:78.5.0-1.el6_102020-11-30redhat
redhatthunderbird-0:78.5.0-1.el8_32020-11-30redhat
redhatthunderbird-0:78.5.0-1.el8_02020-11-30redhat
redhatthunderbird-0:78.5.0-1.el8_12020-11-30redhat
redhatthunderbird-0:78.5.0-1.el8_22020-11-30redhat
redhatthunderbird-0:78.5.0-1.el7_92020-11-30redhat
redhatfirefox-0:78.5.0-1.el7_92020-11-30redhat
redhatfirefox-0:78.5.0-1.el8_32020-11-30redhat
redhatfirefox-0:78.5.0-1.el8_12020-11-30redhat
redhatfirefox-0:78.5.0-1.el8_22020-11-30redhat
redhatthunderbird-0:78.5.0-1.el6_102020-11-30redhat

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

(12 across 6 ecosystems)
Debian:10(2)
PackageVulnerable rangeFixed inDependents
firefox-esr60.7.2esr-1 ... 78.5.0esr-1~deb9u1 (78 versions)78.5.0esr-1~deb10u1—
thunderbird1:60.7.2-1 ... 1:78.5.0-1~deb9u1 (95 versions)1:78.5.0-1~deb10u1—
Debian:11(2)
PackageVulnerable rangeFixed inDependents
firefox-esr—78.5.0esr-1—
thunderbird—1:78.5.0-1—
Debian:12(2)
PackageVulnerable rangeFixed inDependents
firefox-esr—78.5.0esr-1—
thunderbird—1:78.5.0-1—
Debian:13(2)
PackageVulnerable rangeFixed inDependents
firefox-esr—78.5.0esr-1—
thunderbird—1:78.5.0-1—
Debian:14(2)
PackageVulnerable rangeFixed inDependents
firefox-esr—78.5.0esr-1—
thunderbird—1:78.5.0-1—
Debian:9(2)
PackageVulnerable rangeFixed inDependents
firefox-esr45.9.0esr-1 ... 78.4.1esr-2 (185 versions)78.5.0esr-1~deb9u1—
thunderbird1.5-4 ... 1:78.4.2-1~deb9u1 (176 versions)1:78.5.0-1~deb9u1—

Weakness Classification(1)

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

All Vendor Advisories

(15)

Every vendor that published an advisory referencing this CVE — pulled from our cve_vendor_advisories aggregation. Click any row for the vendor's original advisory page.

Data Freshness Timeline

(refreshed 8× in last 7d / 30× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. 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. Most recent first.

Showing the most recent 100 of 122 total refreshes for this CVE.

  1. 2026-08-20 22:52 UTCEPSS rescore
  2. 2026-08-19 17:00 UTCEPSS rescore
  3. 2026-08-18 13:44 UTCEPSS rescore
  4. 2026-08-17 13:43 UTCEPSS rescore
  5. 2026-08-16 14:52 UTCEPSS rescore
  6. 2026-08-16 02:11 UTCEPSS rescore
  7. 2026-08-15 01:26 UTCEPSS rescore
  8. 2026-08-15 00:24 UTCOSV refresh
  9. 2026-08-13 21:57 UTCEPSS rescore
  10. 2026-08-12 13:47 UTCEPSS rescore
  11. 2026-08-09 13:43 UTCEPSS rescore
  12. 2026-08-08 16:33 UTCEPSS rescore
  13. 2026-08-07 16:23 UTCEPSS rescore
  14. 2026-08-06 13:43 UTCEPSS rescore
  15. 2026-08-04 15:06 UTCEPSS rescore
  16. 2026-08-04 10:34 UTCEPSS rescore
  17. 2026-08-02 02:23 UTCEPSS rescore
  18. 2026-08-01 04:12 UTCEPSS rescore
  19. 2026-07-30 16:25 UTCEPSS rescore
  20. 2026-07-30 13:14 UTCOSV refresh
  21. 2026-07-30 01:27 UTCEPSS rescore
  22. 2026-07-28 15:33 UTCEPSS rescore
  23. 2026-07-26 14:51 UTCEPSS rescore
  24. 2026-07-25 14:15 UTCEPSS rescore
  25. 2026-07-24 14:14 UTCEPSS rescore
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  1. 2026-07-23 14:15 UTCEPSS rescore
  2. 2026-07-23 14:15 UTCEPSS rescore
  3. 2026-07-23 01:52 UTCEG score recompute
  4. 2026-07-22 22:38 UTCEG score recompute
  5. 2026-07-22 14:05 UTCEPSS rescore
  6. 2026-07-21 15:22 UTCEPSS rescore
  7. 2026-07-21 15:22 UTCEPSS rescore
  8. 2026-07-20 17:04 UTCEPSS rescore
  9. 2026-07-20 17:04 UTCEPSS rescore
  10. 2026-07-19 14:28 UTCEPSS rescore
  11. 2026-07-19 14:28 UTCEPSS rescore
  12. 2026-07-19 02:26 UTCEPSS rescore
  13. 2026-07-19 02:26 UTCEPSS rescore
  14. 2026-07-16 16:59 UTCEPSS rescore
  15. 2026-07-15 16:55 UTCEPSS rescore
  16. 2026-07-15 16:55 UTCEPSS rescore
  17. 2026-07-15 01:57 UTCEPSS rescore
  18. 2026-07-13 22:27 UTCEPSS rescore
  19. 2026-07-13 22:27 UTCEPSS rescore
  20. 2026-07-13 06:10 UTCEPSS rescore
  21. 2026-07-13 06:10 UTCEPSS rescore
  22. 2026-07-12 22:08 UTCOSV refresh
  23. 2026-07-12 05:44 UTCEPSS rescore
  24. 2026-07-11 08:25 UTCEPSS rescore
  25. 2026-07-11 08:25 UTCEPSS rescore
  26. 2026-07-09 19:07 UTCEPSS rescore
  27. 2026-07-08 15:12 UTCEPSS rescore
  28. 2026-07-07 13:43 UTCEPSS rescore
  29. 2026-07-06 16:25 UTCEPSS rescore
  30. 2026-07-06 16:25 UTCEPSS rescore
  31. 2026-07-06 02:21 UTCEPSS rescore
  32. 2026-07-06 02:21 UTCEPSS rescore
  33. 2026-07-04 06:29 UTCEPSS rescore
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  35. 2026-06-30 23:20 UTCEPSS rescore
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  37. 2026-06-29 14:04 UTCEPSS rescore
  38. 2026-06-28 04:54 UTCEPSS rescore
  39. 2026-06-28 04:54 UTCEPSS rescore
  40. 2026-06-27 03:06 UTCEPSS rescore
  41. 2026-06-27 03:06 UTCEPSS rescore
  42. 2026-06-25 13:48 UTCEPSS rescore
  43. 2026-06-24 14:03 UTCEPSS rescore
  44. 2026-06-24 14:03 UTCEPSS rescore
  45. 2026-06-24 07:59 UTCOSV refresh
  46. 2026-06-23 21:31 UTCEPSS rescore
  47. 2026-06-23 21:31 UTCEPSS rescore
  48. 2026-06-22 14:23 UTCEPSS rescore
  49. 2026-06-22 14:23 UTCEPSS rescore
  50. 2026-06-21 14:54 UTCEPSS rescore
  51. 2026-06-21 14:54 UTCEPSS rescore
  52. 2026-06-21 01:57 UTCEPSS rescore
  53. 2026-06-19 19:24 UTCEPSS rescore
  54. 2026-06-19 19:23 UTCEPSS rescore
  55. 2026-06-18 17:50 UTCEPSS rescore
  56. 2026-06-18 17:50 UTCEPSS rescore
  57. 2026-06-17 17:50 UTCEPSS rescore
  58. 2026-06-16 17:50 UTCEPSS rescore
  59. 2026-06-15 17:46 UTCEPSS rescore
  60. 2026-06-14 23:15 UTCEPSS rescore
  61. 2026-06-13 22:58 UTCEPSS rescore
  62. 2026-06-12 23:10 UTCEPSS rescore
  63. 2026-06-11 13:58 UTCEPSS rescore
  64. 2026-06-10 22:16 UTCEPSS rescore
  65. 2026-06-10 13:20 UTCEPSS rescore
  66. 2026-06-08 14:15 UTCEPSS rescore
  67. 2026-06-07 15:23 UTCEPSS rescore
  68. 2026-06-07 15:23 UTCEPSS rescore
  69. 2026-06-07 15:23 UTCEPSS rescore
  70. 2026-06-07 11:59 UTCOSV refresh
  71. 2026-06-06 13:46 UTCEPSS rescore
  72. 2026-06-06 13:45 UTCEPSS rescore
  73. 2026-06-05 22:45 UTCEPSS rescore
  74. 2026-06-05 22:45 UTCEPSS rescore
  75. 2026-06-05 06:08 UTCEPSS rescore

Related CVEs(same vendor + same CWE)

Frequently asked(5)

What is CVE-2020-26958?
CVE-2020-26958 is a medium vulnerability published on December 9, 2020. Firefox did not block execution of scripts with incorrect MIME types when the response was intercepted and cached through a ServiceWorker. This could lead to a cross-site script inclusion vulnerability, or a Content Security Policy bypass. This vulnerability affects Firefox < 83, Firefox ESR <…
When was CVE-2020-26958 disclosed?
CVE-2020-26958 was first published in the National Vulnerability Database on December 9, 2020, with the most recent update on November 21, 2024. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2020-26958 actively exploited?
CVE-2020-26958 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 1% probability of exploitation in the next 30 days, which ranks it in the top 31.7% of all scored CVEs.
What is the CVSS score of CVE-2020-26958?
CVE-2020-26958 has a CVSS v3 base score of 6.1 (NVD).
How do I remediate CVE-2020-26958?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2020-26958, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

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