CVE-2021-23991

MEDIUMNVD 6.86.8—
EchelonGraph scoreMEDIUM confidence

This medium-severity CVE scores 6.8 under NVD CVSS v3. EPSS exploit probability: 1.0% (62nd percentile of EPSS-scored CVEs). 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
6.8EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 1.0%CVSS: 6.8Exploit: None knownExposed services: Not assessed

A fix is available — apply it.

If a Thunderbird user has previously imported Alice's OpenPGP key, and Alice has extended the validity period of her key, but Alice's updated key has not yet been imported, an attacker may send an email containing a crafted version of Alice's key with an invalid subkey, Thunderbird might subsequently attempt to use the invalid subkey, and will fail to send encrypted email to Alice. This vulnerability affects Thunderbird < 78.9.1.

CVSS v3
6.8
EG Score
6.8MEDIUMmedium confidence
EG Risk
36
EG Risk 36/100CISA SSVC

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
Severity68% × 45%
Exploitation1% × 40%
Automatability30% × 15%
CISA SSVC: Track at low or medium mission impact; Track or Attend at high (mission-essential systems).
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
1.0%
EPSS %ILE
62nd
KEV
Not listed

CISA SSVCTrack at low or medium mission impact; Track or 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 (no KEV listing, exploit record or EPSS ≥ 50%) · Automatable unknown (not published for this CVE) · Technical impact partial (CVSS below 9.0). Mission impact is CISA's Mission & Well-being decision point, and only you can judge it: high means the affected system is essential to your organisation's mission, or its compromise could cause irreversible harm to people. CISA's decision table

Published

June 24, 2021

Last Modified

November 21, 2024

References (4)

Patch Availability(6)

Vendor / EcosystemFix (by version range) / PatchReleasedSource
ubuntuxul-ext-lightning (1:78.11.0+build1-0ubuntu0.21.04.2) @ hirsute2026-05-26ubuntu
ubuntuxul-ext-lightning (1:78.11.0+build1-0ubuntu0.18.04.2) @ bionic2026-05-26ubuntu
redhatthunderbird-0:78.9.1-1.el8_12021-04-14redhat
redhatthunderbird-0:78.9.1-1.el8_22021-04-14redhat
redhatthunderbird-0:78.9.1-1.el7_92021-04-14redhat
redhatthunderbird-0:78.9.1-1.el8_32021-04-14redhat

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

(6 across 6 ecosystems)
Debian:10(1)
PackageVulnerable rangeFix by version rangeDependents
thunderbird1:60.7.2-1 ... 1:78.9.0-1~deb9u1 (115 versions)
  • every version up to 1:78.10.0-1~deb10u1: fixed in 1:78.10.0-1~deb10u1
—
Debian:11(1)
PackageVulnerable rangeFix by version rangeDependents
thunderbird—
  • every version up to 1:78.10.0-1: fixed in 1:78.10.0-1
—
Debian:12(1)
PackageVulnerable rangeFix by version rangeDependents
thunderbird—
  • every version up to 1:78.10.0-1: fixed in 1:78.10.0-1
—
Debian:13(1)
PackageVulnerable rangeFix by version rangeDependents
thunderbird—
  • every version up to 1:78.10.0-1: fixed in 1:78.10.0-1
—
Debian:14(1)
PackageVulnerable rangeFix by version rangeDependents
thunderbird—
  • every version up to 1:78.10.0-1: fixed in 1:78.10.0-1
—
Debian:9(1)
PackageVulnerable rangeFix by version rangeDependents
thunderbird1.5-4 ... 1:78.9.0-1~deb9u1 (196 versions)
  • every version up to 1:78.10.0-1~deb9u1: fixed in 1:78.10.0-1~deb9u1
—

All Vendor Advisories

(6)

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 / 34× 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 181 total refreshes for this CVE.

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

Related CVEs(same product + same vendor)

Frequently asked(5)

What is CVE-2021-23991?
CVE-2021-23991 is a medium vulnerability published on June 24, 2021. If a Thunderbird user has previously imported Alice's OpenPGP key, and Alice has extended the validity period of her key, but Alice's updated key has not yet been imported, an attacker may send an email containing a crafted version of Alice's key with an invalid subkey, Thunderbird might…
When was CVE-2021-23991 disclosed?
CVE-2021-23991 was first published 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-2021-23991 actively exploited?
CVE-2021-23991 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 1.0% probability of exploitation in the next 30 days (62nd percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2021-23991?
CVE-2021-23991 has a CVSS v3 base score of 6.8 (NVD).
How do I remediate CVE-2021-23991?
A fix for CVE-2021-23991 is available: update to the fixed version the vendor names in its advisory.

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