CVE-2021-29984

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.

Instruction reordering resulted in a sequence of instructions that would cause an object to be incorrectly considered during garbage collection. This led to memory corruption and a potentially exploitable crash. This vulnerability affects Thunderbird < 78.13, Thunderbird < 91, Firefox ESR < 78.13, and Firefox < 91.

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
69%
KEV
Not listed

Published

August 17, 2021

Last Modified

November 21, 2024

Advisory Details (7)

Auto-updated Jul 26, 2026
No patch confirmed yet.
generic

Mozilla Thunderbird: Multiple Vulnerabilities (GLSA 202208-14) — Gentoo security

https://security.gentoo.org/glsa/202208-14
generic

Mozilla Firefox: Multiple vulnerabilities (GLSA 202202-03) — Gentoo security

https://security.gentoo.org/glsa/202202-03
generic

1720031 - (CVE-2021-29984) Assertion failure: !IsInsideNursery(thing) at AtomMarking.cpp:206

https://bugzilla.mozilla.org/show_bug.cgi?id=1720031
generic

Security Vulnerabilities fixed in Thunderbird 91 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2021-36/
generic

Security Vulnerabilities fixed in Thunderbird 78.13 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2021-35/
generic

Security Vulnerabilities fixed in Firefox ESR 78.13 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2021-34/
generic

Security Vulnerabilities fixed in Firefox 91 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2021-33/

Vendor Advisories for CVE-2021-29984(2)

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

Patch Availability(10)

Vendor / EcosystemFixed in / PatchReleasedSource
ubuntufirefox-mozsymbols (91.0+build2-0ubuntu0.20.04.1) @ focal2026-05-26ubuntu
ubuntuthunderbird-locale-id (1:78.13.0+build1-0ubuntu0.20.04.2) @ focal2026-05-26ubuntu
redhatfirefox-0:78.13.0-2.el7_92021-08-16redhat
redhatthunderbird-0:78.13.0-1.el7_92021-08-16redhat
redhatthunderbird-0:78.13.0-1.el8_42021-08-16redhat
redhatfirefox-0:78.13.0-2.el8_42021-08-16redhat
redhatfirefox-0:78.13.0-2.el8_12021-08-16redhat
redhatthunderbird-0:78.13.0-1.el8_12021-08-16redhat
redhatfirefox-0:78.13.0-2.el8_22021-08-16redhat
redhatthunderbird-0:78.13.0-1.el8_22021-08-16redhat

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.

Weakness Classification(1)

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

Additional Vendor Advisories

(8)

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 12× in last 7d / 48× 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 106 total refreshes for this CVE.

  1. 2026-07-26 14:52 UTCEPSS rescore
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Frequently asked(5)

What is CVE-2021-29984?
CVE-2021-29984 is a high vulnerability published on August 17, 2021. Instruction reordering resulted in a sequence of instructions that would cause an object to be incorrectly considered during garbage collection. This led to memory corruption and a potentially exploitable crash. This vulnerability affects Thunderbird < 78.13, Thunderbird < 91, Firefox ESR < 78.13,…
When was CVE-2021-29984 disclosed?
CVE-2021-29984 was first published in the National Vulnerability Database on August 17, 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-2021-29984 actively exploited?
CVE-2021-29984 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 30.6% of all scored CVEs.
What is the CVSS score of CVE-2021-29984?
CVE-2021-29984 has a CVSS v3 base score of 8.8 (NVD).
How do I remediate CVE-2021-29984?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-29984, 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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