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CVE Record

CVE-2021-29970: A malicious webpage could have triggered a use-after-free, memory corruption, and a potentially exploitable...

A malicious webpage could have triggered a use-after-free, memory corruption, and a potentially exploitable crash. *This bug could only be triggered when accessibility was enabled.*. This vulnerability affects Thunderbird < 78.12, Firefox ESR < 78.12, and Firefox < 90.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

CVE-2021-29970 is a Mozilla browser and mail-client memory safety bug. A malicious webpage could trigger memory corruption and a potentially exploitable crash, but only when accessibility support was enabled. The exposed products are older Firefox, Firefox ESR, and Thunderbird versions below the fixed release levels named in the CVE record.

Executive priority

Prioritize remediation for any remaining legacy Mozilla installations, particularly on user workstations that browse the web. The issue has serious memory-corruption characteristics, but available sources do not show known active exploitation and the trigger requires accessibility support.

Technical view

The flaw is described as a use-after-free leading to memory corruption and a potentially exploitable crash. The trigger path requires accessibility to be enabled. Affected versions are Thunderbird before 78.12, Firefox ESR before 78.12, and Firefox before 90. No CVSS, CWE, or detailed exploit mechanics are provided in the bundle.

Likely exposure

Exposure is most likely on endpoints still running Firefox below 90, Firefox ESR below 78.12, or Thunderbird below 78.12, especially where accessibility features or assistive technologies are enabled. Current managed browser fleets should mainly treat this as legacy-version exposure.

Exploitation context

The source bundle supports a malicious-webpage trigger and a potentially exploitable crash. It does not show CISA KEV listing, active exploitation, public exploit availability, or confirmed code execution. The accessibility requirement materially narrows the trigger conditions.

Researcher notes

Bugzilla and Mozilla advisories are referenced, but the bundle does not include CVSS, CWE, exploit details, or proof of active exploitation. Keep analysis bounded to the documented use-after-free, accessibility trigger condition, and fixed-version thresholds.

Mitigation direction

  • Upgrade Firefox to version 90 or later where applicable.
  • Upgrade Firefox ESR to version 78.12 or later.
  • Upgrade Thunderbird to version 78.12 or later.
  • Check Mozilla and OS vendor advisories for supported package guidance.
  • Prioritize endpoints using accessibility features or assistive technologies.

Validation and detection

  • Inventory Firefox, Firefox ESR, and Thunderbird versions across endpoints.
  • Flag Firefox versions below 90 as affected.
  • Flag Firefox ESR and Thunderbird versions below 78.12 as affected.
  • Identify systems where accessibility support is enabled.
  • Confirm vendor-managed packages include the relevant Mozilla security fixes.
Prepared
Confidence
high
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-2021-29970 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
7Source 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
MozillaThunderbirdunspecifiedListed
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.