Security readout for executives and security teams
Plain-English summary
This is a Windows-only Mozilla issue where a malicious program already installed on the same machine could make Firefox process an interprocess message incorrectly, causing an out-of-bounds read. The sources do not show remote exploitation or active exploitation.
Executive priority
Treat this as a routine but necessary endpoint patching item. It is not described as remotely exploitable or actively exploited, but stale browser and mail-client versions on Windows increase avoidable local compromise risk.
Technical view
CVE-2021-29964 concerns incorrect processing of Windows WM_COPYDATA messages, leading to an out-of-bounds read. Mozilla states it affects Firefox before 89, Firefox ESR before 78.11, and Thunderbird before 78.11. Other operating systems are unaffected.
Likely exposure
Exposure is limited to Windows endpoints running affected Mozilla versions: Firefox before 89, Firefox ESR before 78.11, or Thunderbird before 78.11. Non-Windows systems are not affected according to the CVE description.
Exploitation context
The attacker model requires a locally installed hostile program. The provided sources do not cite CISA KEV listing, public exploitation, or remote exploitation. Impact details beyond out-of-bounds read are limited.
Researcher notes
Evidence is sparse: no CVSS, CWE, or detailed public impact is included in the bundle. The key technical facts are Windows-only scope, local hostile-program prerequisite, WM_COPYDATA handling, and out-of-bounds read behavior.
Mitigation direction
- Upgrade Firefox to version 89 or later on Windows systems.
- Upgrade Firefox ESR and Thunderbird to version 78.11 or later.
- Retire unsupported Mozilla installations where upgrades are unavailable.
- Review Mozilla advisories MFSA2021-23, MFSA2021-24, and MFSA2021-26.
Validation and detection
- Inventory Windows endpoints for Firefox, Firefox ESR, and Thunderbird versions.
- Flag Firefox below 89 as affected.
- Flag Firefox ESR or Thunderbird below 78.11 as affected.
- Confirm non-Windows assets are excluded from this CVE’s scope.
- Document remediation status for legacy or unsupported installations.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
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
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CVE-2021-29964 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Unknown
- CVSS
- Not scored
- Known Exploited
- No
- Published
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.
CVSS and timeline data
No CVSS vectors or timeline events were available in the normalized CVE source material.
Source materials
- CVE List V5 sourceCVE List V5
- https://www.mozilla.org/security/advisories/mfsa2021-26/CVE reference · x_refsource_MISC
- https://www.mozilla.org/security/advisories/mfsa2021-24/CVE reference · x_refsource_MISC
- https://www.mozilla.org/security/advisories/mfsa2021-23/CVE reference · x_refsource_MISC
- https://bugzilla.mozilla.org/show_bug.cgi?id=1706501CVE reference · x_refsource_MISC
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.