CVE-2021-23999

HIGHNVD 8.88.8—
EchelonGraph scoreMEDIUM confidence

Score 8.8 from GitHub Security Advisory (severity: HIGH) published 2022-05-24. NVD baseline CVSS 8.8; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, nvd
8.8EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 1%CVSS: 8.8Exploit: None knownExposed: 0

A fix is available — apply it.

If a Blob URL was loaded through some unusual user interaction, it could have been loaded by the System Principal and granted additional privileges that should not be granted to web content. This vulnerability affects Firefox ESR < 78.10, Thunderbird < 78.10, and Firefox < 88.

CVSS v3
8.8
EG Score
8.8(medium)
EG Risk
45(Track)
EG Risk 45/100SSVC: 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
Severity88% × 45%
Exploitation1% × 40%
Automatability30% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
1%
EPSS %ILE
71%
KEV
Not listed

Published

June 24, 2021

Last Modified

November 21, 2024

Advisory Details (4)

Auto-updated Aug 4, 2026
🔬 Proof of concept available. No patch confirmed yet.
generic

Security Vulnerabilities fixed in Firefox 88 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2021-16/
generic

Security Vulnerabilities fixed in Firefox ESR 78.10 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2021-15/
generic

Security Vulnerabilities fixed in Thunderbird 78.10 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2021-14/
generic🟡 PoC Available

1691153 - (CVE-2021-23999) Blob URLs loaded by system principal may be given the incorrect principal

https://bugzilla.mozilla.org/show_bug.cgi?id=1691153

Patch Availability(11)

Vendor / EcosystemFixed in / PatchReleasedSource
ubuntufirefox-mozsymbols (88.0+build2-0ubuntu0.20.10.1) @ groovy2026-05-26ubuntu
ubuntuxul-ext-lightning (1:78.11.0+build1-0ubuntu0.20.10.2) @ groovy2026-05-26ubuntu
ubuntuxul-ext-lightning (1:78.11.0+build1-0ubuntu0.18.04.2) @ bionic2026-05-26ubuntu
redhatfirefox-0:78.10.0-1.el8_32021-04-26redhat
redhatthunderbird-0:78.10.0-1.el8_12021-04-26redhat
redhatfirefox-0:78.10.0-1.el8_12021-04-26redhat
redhatthunderbird-0:78.10.0-1.el8_22021-04-26redhat
redhatfirefox-0:78.10.0-1.el8_22021-04-26redhat
redhatthunderbird-0:78.10.0-1.el7_92021-04-26redhat
redhatfirefox-0:78.10.0-1.el7_92021-04-26redhat
redhatthunderbird-0:78.10.0-1.el8_32021-04-26redhat

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

(12 across 6 ecosystems)
Debian:10(2)
PackageVulnerable rangeFixed inDependents
firefox-esr60.7.2esr-1 ... 78.9.0esr-1~deb9u1 (96 versions)78.10.0esr-1~deb10u1—
thunderbird1:60.7.2-1 ... 1:78.9.0-1~deb9u1 (115 versions)1:78.10.0-1~deb10u1—
Debian:11(2)
PackageVulnerable rangeFixed inDependents
firefox-esr—78.10.0esr-1—
thunderbird—1:78.10.0-1—
Debian:12(2)
PackageVulnerable rangeFixed inDependents
firefox-esr—78.10.0esr-1—
thunderbird—1:78.10.0-1—
Debian:13(2)
PackageVulnerable rangeFixed inDependents
firefox-esr—78.10.0esr-1—
thunderbird—1:78.10.0-1—
Debian:14(2)
PackageVulnerable rangeFixed inDependents
firefox-esr—78.10.0esr-1—
thunderbird—1:78.10.0-1—
Debian:9(2)
PackageVulnerable rangeFixed inDependents
firefox-esr45.9.0esr-1 ... 78.9.0esr-1~deb9u1 (203 versions)78.10.0esr-1~deb9u1—
thunderbird1.5-4 ... 1:78.9.0-1~deb9u1 (196 versions)1:78.10.0-1~deb9u1—

Weakness Classification(2)

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

All Vendor Advisories

(11)

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 7× in last 7d / 29× 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 160 total refreshes for this CVE.

  1. 2026-09-18 19:23 UTCEPSS rescore
  2. 2026-09-17 19:23 UTCEPSS rescore
  3. 2026-09-16 14:05 UTCEPSS rescore
  4. 2026-09-16 14:04 UTCEPSS rescore
  5. 2026-09-15 03:06 UTCEPSS rescore
  6. 2026-09-13 16:43 UTCEPSS rescore
  7. 2026-09-12 14:57 UTCEPSS rescore
  8. 2026-09-11 09:33 UTCEPSS rescore
  9. 2026-09-10 09:29 UTCEPSS rescore
  10. 2026-09-08 21:56 UTCEPSS rescore
  11. 2026-09-07 15:58 UTCEPSS rescore
  12. 2026-09-06 13:44 UTCEPSS rescore
  13. 2026-09-06 13:44 UTCEPSS rescore
  14. 2026-09-06 13:39 UTCOSV refresh
  15. 2026-09-05 15:25 UTCEPSS rescore
  16. 2026-09-04 13:57 UTCEPSS rescore
  17. 2026-09-04 05:03 UTCEPSS rescore
  18. 2026-09-02 14:08 UTCEPSS rescore
  19. 2026-09-01 13:50 UTCEPSS rescore
  20. 2026-09-01 03:32 UTCEPSS rescore
  21. 2026-08-30 19:14 UTCEPSS rescore
  22. 2026-08-30 01:19 UTCEPSS rescore
  23. 2026-08-28 21:37 UTCEPSS rescore
  24. 2026-08-27 14:22 UTCEPSS rescore
  25. 2026-08-26 14:42 UTCEPSS rescore
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  1. 2026-08-25 13:45 UTCEPSS rescore
  2. 2026-08-23 00:16 UTCEPSS rescore
  3. 2026-08-21 23:46 UTCEPSS rescore
  4. 2026-08-20 22:52 UTCEPSS rescore
  5. 2026-08-20 00:15 UTCOSV refresh
  6. 2026-08-19 17:01 UTCEPSS rescore
  7. 2026-08-18 13:45 UTCEPSS rescore
  8. 2026-08-17 13:43 UTCEPSS rescore
  9. 2026-08-16 14:52 UTCEPSS rescore
  10. 2026-08-16 02:11 UTCEPSS rescore
  11. 2026-08-15 01:27 UTCEPSS rescore
  12. 2026-08-13 21:57 UTCEPSS rescore
  13. 2026-08-12 13:47 UTCEPSS rescore
  14. 2026-08-11 13:38 UTCEPSS rescore
  15. 2026-08-09 13:43 UTCEPSS rescore
  16. 2026-08-08 16:33 UTCEPSS rescore
  17. 2026-08-07 16:23 UTCEPSS rescore
  18. 2026-08-06 13:43 UTCEPSS rescore
  19. 2026-08-05 19:14 UTCEPSS rescore
  20. 2026-08-04 19:27 UTCOSV refresh
  21. 2026-08-04 15:06 UTCEPSS rescore
  22. 2026-08-04 10:34 UTCEPSS rescore
  23. 2026-08-03 10:32 UTCEPSS rescore
  24. 2026-08-02 02:24 UTCEPSS rescore
  25. 2026-08-01 04:12 UTCEPSS rescore
  26. 2026-07-30 16:25 UTCEPSS rescore
  27. 2026-07-30 01:27 UTCEPSS rescore
  28. 2026-07-30 01:27 UTCEPSS rescore
  29. 2026-07-26 14:52 UTCEPSS rescore
  30. 2026-07-25 14:15 UTCEPSS rescore
  31. 2026-07-24 14:15 UTCEPSS rescore
  32. 2026-07-23 14:15 UTCEPSS rescore
  33. 2026-07-23 01:58 UTCEG score recompute
  34. 2026-07-22 22:44 UTCEG score recompute
  35. 2026-07-22 14:05 UTCEPSS rescore
  36. 2026-07-21 15:22 UTCEPSS rescore
  37. 2026-07-21 15:22 UTCEPSS rescore
  38. 2026-07-20 17:04 UTCEPSS rescore
  39. 2026-07-19 02:26 UTCEPSS rescore
  40. 2026-07-18 17:59 UTCOSV refresh
  41. 2026-07-18 10:02 UTCEPSS rescore
  42. 2026-07-16 17:00 UTCEPSS rescore
  43. 2026-07-15 16:55 UTCEPSS rescore
  44. 2026-07-15 16:55 UTCEPSS rescore
  45. 2026-07-15 01:57 UTCEPSS rescore
  46. 2026-07-13 22:27 UTCEPSS rescore
  47. 2026-07-13 22:27 UTCEPSS rescore
  48. 2026-07-13 06:10 UTCEPSS rescore
  49. 2026-07-13 06:10 UTCEPSS rescore
  50. 2026-07-12 05:44 UTCEPSS rescore
  51. 2026-07-12 05:44 UTCEPSS rescore
  52. 2026-07-11 08:25 UTCEPSS rescore
  53. 2026-07-09 19:07 UTCEPSS rescore
  54. 2026-07-08 15:12 UTCEPSS rescore
  55. 2026-07-07 13:43 UTCEPSS rescore
  56. 2026-07-06 16:25 UTCEPSS rescore
  57. 2026-07-06 02:21 UTCEPSS rescore
  58. 2026-07-06 02:21 UTCEPSS rescore
  59. 2026-07-05 02:28 UTCEPSS rescore
  60. 2026-07-05 02:28 UTCEPSS rescore
  61. 2026-07-04 06:29 UTCEPSS rescore
  62. 2026-07-04 06:29 UTCEPSS rescore
  63. 2026-07-02 16:57 UTCEPSS rescore
  64. 2026-07-01 15:03 UTCEPSS rescore
  65. 2026-07-01 00:48 UTCOSV refresh
  66. 2026-06-30 23:20 UTCEPSS rescore
  67. 2026-06-30 23:20 UTCEPSS rescore
  68. 2026-06-29 14:04 UTCEPSS rescore
  69. 2026-06-29 14:04 UTCEPSS rescore
  70. 2026-06-28 14:05 UTCEPSS rescore
  71. 2026-06-28 04:54 UTCEPSS rescore
  72. 2026-06-28 04:54 UTCEPSS rescore
  73. 2026-06-27 03:06 UTCEPSS rescore
  74. 2026-06-27 03:06 UTCEPSS rescore
  75. 2026-06-25 13:48 UTCEPSS rescore

Related CVEs(same vendor + same CWE)

Frequently asked(5)

What is CVE-2021-23999?
CVE-2021-23999 is a high vulnerability published on June 24, 2021. If a Blob URL was loaded through some unusual user interaction, it could have been loaded by the System Principal and granted additional privileges that should not be granted to web content. This vulnerability affects Firefox ESR < 78.10, Thunderbird < 78.10, and Firefox < 88.
When was CVE-2021-23999 disclosed?
CVE-2021-23999 was first published in the National Vulnerability Database on June 24, 2021, 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-2021-23999 actively exploited?
CVE-2021-23999 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 29.3% of all scored CVEs.
What is the CVSS score of CVE-2021-23999?
CVE-2021-23999 has a CVSS v3 base score of 8.8 (NVD).
How do I remediate CVE-2021-23999?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-23999, 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

See which npm, PyPI, Go, and Maven packages are affected by CVE-2021-23999

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