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CVE Record

CVE-2026-0891: Memory safety bugs fixed in Firefox ESR 140.7, Thunderbird ESR 140.7, Firefox 147 and Thunderbird 147

Memory safety bugs present in Firefox ESR 140.6, Thunderbird ESR 140.6, Firefox 146 and Thunderbird 146. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability was fixed in Firefox 147, Firefox ESR 140.7, Thunderbird 147, and Thunderbird 140.7.

HighCVSS 8.1Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

Mozilla fixed memory safety bugs in Firefox and Thunderbird. The source says some showed memory corruption and could potentially allow arbitrary code execution with enough effort. Treat this as a high-priority browser and email-client update, especially for managed endpoints and Linux package fleets.

Executive priority

Prioritize normal emergency browser and email-client patching. The issue has high impact and plausible code execution risk, but the provided sources do not show active exploitation.

Technical view

CVE-2026-0891 is a CWE-119 memory safety issue affecting Firefox 146, Firefox ESR 140.6, Thunderbird 146, and Thunderbird ESR 140.6 per the description. Mozilla fixed it in Firefox 147, Firefox ESR 140.7, Thunderbird 147, and Thunderbird ESR 140.7. CVSS is 8.1 with high confidentiality, integrity, and availability impact.

Likely exposure

Exposure is likely on endpoints or servers with vulnerable Mozilla Firefox or Thunderbird builds, including downstream Red Hat-packaged deployments referenced by listed advisories. The bundle does not identify other affected products.

Exploitation context

The bundle does not show CISA KEV listing or cited evidence of active exploitation. Mozilla states some bugs showed memory corruption and may be exploitable for arbitrary code execution with enough effort. CVSS lists attack complexity as high.

Researcher notes

The public bundle groups multiple memory safety bugs under Mozilla advisories and Bugzilla IDs. Details are limited, so validation should focus on version/package state rather than exploit reproduction. Do not assume affected products beyond Mozilla Firefox, Thunderbird, and listed downstream Red Hat tracking.

Mitigation direction

  • Upgrade Firefox to 147 or Firefox ESR 140.7 where applicable.
  • Upgrade Thunderbird to 147 or Thunderbird ESR 140.7 where applicable.
  • Apply relevant Red Hat errata for packaged Mozilla components.
  • If immediate patching is blocked, check vendor guidance for temporary mitigations.

Validation and detection

  • Inventory Firefox and Thunderbird versions across managed endpoints.
  • Confirm vulnerable builds are not present: Firefox 146, ESR 140.6, Thunderbird 146, ESR 140.6.
  • Check Linux package status against applicable Red Hat advisories.
  • Verify vulnerability scanners map findings to CVE-2026-0891 after updates.
Prepared
Confidence
high
Sources
12

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

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cwe · low confidence lookup

CWE-119: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

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description · low confidence lookup

Execution behavior lookup

The CVE wording references code or command execution, so execution technique review may help defensive triage. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.

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cve · low confidence lookup

CVE-2026-0891 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

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Vulnerability profileCVE Program record
Severity
High
CVSS
8.1 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

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.

2CVSS vectors
5Timeline events
2ADP providers
32Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: noTechnical Impact: total

CVSS vector scores

2 official scores

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
8.1CVSS 3.1HighCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H2.25.9CISA-ADP
7.5CVSS 3.1HighCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H1.65.9redhat-SADP

Vulnerability scoring details

Base CVSS 3.1 score

8.1High
CVSS 3.1 vector shape for CVE-2026-0891Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. ADP timelineredhat-SADP

    Made public.

  3. CVE publishedCVE Program

    The CVE record was published.

  4. ADP timelineredhat-SADP

    Reported to Red Hat.

  5. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
cvssV3_1other:ssvc
redhat-SADPfirefox: thunderbird: Memory safety bugs fixed in Firefox ESR 140.7, Thunderbird ESR 140.7, Firefox 147 and Thunderbird 147
other:Red Hat severity ratingcvssV3_1
  • 2026-01-13T14:01:25.941Z: Reported to Red Hat.
  • 2026-01-13T13:30:59.454Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
MozillaFirefox140.7, 147Listed
MozillaThunderbird140.7, 147Listed
Weakness

CWE details

CWE-119

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

CWE-119 · source CWE mapping

Improper Restriction of Operations within the Bounds of a Memory Buffer

Improper Restriction of Operations within the Bounds of a Memory Buffer represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

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