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CVE Record

CVE-2021-29985: A use-after-free vulnerability in media channels could have led to memory corruption and a potentially expl...

A use-after-free vulnerability in media channels could have led to memory corruption and a potentially exploitable crash. This vulnerability affects Thunderbird < 78.13, Thunderbird < 91, Firefox ESR < 78.13, and Firefox < 91.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

CVE-2021-29985 is a Mozilla media-channel use-after-free issue that could cause memory corruption and a potentially exploitable crash. It affects older Firefox, Firefox ESR, and Thunderbird releases. The main business risk is continued use of outdated browsers or mail clients, especially where legacy ESR versions remain deployed.

Executive priority

Prioritize remediation where outdated Mozilla clients are used for browsing, email, or processing untrusted media. There is no supplied evidence of active exploitation, but browser and mail-client memory corruption issues can become high-impact if legacy versions persist.

Technical view

Mozilla describes a use-after-free vulnerability in media channels affecting Firefox before 91, Firefox ESR before 78.13, Thunderbird before 78.13, and Thunderbird before 91. The supplied record does not include CVSS, CWE, confirmed exploitability details, or exploitation evidence.

Likely exposure

Exposure is most likely on endpoints or servers running unsupported Mozilla Firefox, Firefox ESR, or Thunderbird versions below the fixed release lines named by Mozilla. Linux distributions may have separately backported fixes, so package status should be checked against vendor advisories.

Exploitation context

The source bundle does not show CISA KEV listing or cited evidence of active exploitation. Public descriptions say the crash was potentially exploitable, but they do not provide confirmed in-the-wild exploitation in the supplied material.

Researcher notes

Evidence is strong for affected products and fixed version thresholds, but incomplete for severity scoring and exploit status. Treat downstream package versions carefully because distributions may backport fixes without matching Mozilla upstream version numbers.

Mitigation direction

  • Upgrade Firefox to 91 or later where applicable.
  • Upgrade Firefox ESR to 78.13 or later where applicable.
  • Upgrade Thunderbird to 78.13, 91, or later as appropriate.
  • For Gentoo systems, follow the referenced GLSA package guidance.
  • Check Mozilla advisories for current vendor-specific remediation details.

Validation and detection

  • Inventory installed Firefox, Firefox ESR, and Thunderbird versions.
  • Flag any installation below the affected-version thresholds.
  • Confirm distribution packages include the Mozilla security fix or backport.
  • Review endpoint management data for legacy ESR or unmanaged mail clients.
  • Document exceptions where upgrades are blocked and track remediation owners.
Prepared
Confidence
medium
Sources
8

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

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CVE-2021-29985 mapping review

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
0Timeline events
0ADP providers
8Source links

CVSS and timeline data

No CVSS vectors or timeline events were available in the normalized CVE source material.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
MozillaThunderbirdunspecified, unspecifiedListed
MozillaFirefox ESRunspecifiedListed
MozillaFirefoxunspecifiedListed
Weakness

CWE details

No CWE listed

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.