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CVE Record

CVE-2026-0877: Mitigation bypass in the DOM: Security component

Mitigation bypass in the DOM: Security component. This vulnerability was fixed in Firefox 147, Firefox ESR 115.32, 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

CVE-2026-0877 is a high-severity Mozilla issue where a browser or mail client security mitigation could be bypassed in DOM handling. Mozilla says it is fixed in Firefox 147, Firefox ESR 115.32/140.7, Thunderbird 147, and Thunderbird 140.7. User interaction is required, but successful exploitation could affect confidentiality and integrity.

Executive priority

Treat this as a near-term endpoint patching priority. It affects widely deployed browser and email software, has high confidentiality and integrity impact, and requires user interaction rather than privileged access. Prioritize managed desktop fleets and Linux package channels.

Technical view

The issue is classified as CWE-693, a protection mechanism failure in Mozilla’s DOM: Security component. The CVSS 3.1 vector is AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N, indicating remote reachability, low attack complexity, no privileges, required user interaction, and high confidentiality and integrity impact.

Likely exposure

Exposure is most likely on endpoints using Firefox, Firefox ESR, or Thunderbird that have not reached the Mozilla fixed releases, including systems receiving these packages through Red Hat channels. The bundle does not identify specific pre-fixed version ranges beyond the named fixed releases.

Exploitation context

The source bundle does not show CISA KEV listing or cited evidence of active exploitation. The scoring indicates a plausible remote attack path requiring a user action, such as interacting with malicious content, but no exploit details are provided in the sources.

Researcher notes

Useful research focus is version validation and advisory correlation, not exploit reproduction. The public bundle gives CVSS, CWE, affected Mozilla products, fixed releases, and Red Hat advisory links, but does not provide technical root-cause detail or confirmed exploitation evidence.

Mitigation direction

  • Update Firefox to 147 or later where applicable.
  • Update Firefox ESR to 115.32 or 140.7 or later.
  • Update Thunderbird to 147 or 140.7 or later.
  • Apply relevant Red Hat security advisories for managed Linux packages.
  • Check Mozilla and Red Hat guidance for channel-specific fixes.

Validation and detection

  • Inventory installed Firefox, Firefox ESR, and Thunderbird versions across endpoints.
  • Confirm versions meet or exceed the Mozilla fixed releases.
  • Verify Red Hat errata are applied where Red Hat packages are used.
  • Check vulnerability tooling no longer flags CVE-2026-0877 after updates.
  • Confirm unsupported or unmanaged browser installs are included in endpoint coverage.
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-693: 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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cve · low confidence lookup

CVE-2026-0877 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:L/PR:N/UI:R/S:U/C:H/I:H/A:N

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
33Source links

SSVC decision data

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

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:L/PR:N/UI:R/S:U/C:H/I:H/A:N2.85.2CISA-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-2026-0877Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

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

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: Mitigation bypass in the DOM: Security component
other:Red Hat severity ratingcvssV3_1
  • 2026-01-13T14:01:52.660Z: Reported to Red Hat.
  • 2026-01-13T13:30:52.979Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
MozillaFirefox115.32, 140.7, 147Listed
MozillaThunderbird140.7, 147Listed
Weakness

CWE details

CWE-693

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

CWE-693 · source CWE mapping

Protection Mechanism Failure

Protection Mechanism Failure represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

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