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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 flaws in Firefox and Thunderbird that could corrupt memory. Mozilla says some issues may be exploitable for arbitrary code execution with enough effort. No provided source shows active exploitation.

Executive priority

Treat as a high-priority patching item for browsers and mail clients. The business risk is credible code execution exposure, but the bundle does not support an emergency active-exploitation claim.

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. It is rated CVSS 8.1 high and fixed in Firefox 147, Firefox ESR 140.7, Thunderbird 147, and Thunderbird ESR 140.7.

Likely exposure

Exposure is most likely on desktops, servers, or managed images still running the listed pre-fix Mozilla browser or mail client versions, including downstream Red Hat-packaged builds covered by referenced errata.

Exploitation context

The bundle states KEV is false. Mozilla describes memory corruption and presumed arbitrary code execution potential, but the provided sources do not cite active exploitation, public exploit code, or confirmed weaponization.

Researcher notes

The record groups multiple Mozilla memory safety bugs and Bugzilla IDs. Detailed bug evidence may be incomplete or restricted, so validation should focus on version/package state and vendor advisories, not exploit reproduction.

Mitigation direction

  • Upgrade Firefox to 147 or Firefox ESR to 140.7 wherever deployed.
  • Upgrade Thunderbird to 147 or Thunderbird ESR to 140.7 wherever deployed.
  • Apply applicable Red Hat security errata for Mozilla packages.
  • Check Mozilla and OS vendor advisories for environment-specific package guidance.

Validation and detection

  • Inventory Firefox and Thunderbird versions across endpoints and server images.
  • Confirm no Firefox 146, Firefox ESR 140.6, Thunderbird 146, or Thunderbird ESR 140.6 remain.
  • Verify Red Hat systems have the relevant RHSA updates installed.
  • Review vulnerability scanner findings against Mozilla fixed-version data.
Prepared
Confidence
medium
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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