LiveActive security incident?Get immediate response
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
Discuss exposureBack to CVEs
Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

CVE-2026-0877 is a high-severity Mozilla vulnerability involving a bypass of a DOM security mitigation. A victim would need to interact with malicious content, but successful exploitation could expose sensitive information or allow unauthorized content changes. Mozilla lists fixes in Firefox 147, Firefox ESR 115.32 and 140.7, Thunderbird 147, and Thunderbird 140.7.

Executive priority

Prioritize patching in normal high-severity browser and email-client update cycles, especially for users exposed to untrusted web content or email. There is no provided evidence of active exploitation, but the confidentiality and integrity impacts justify timely remediation.

Technical view

The issue is classified as CWE-693, protection mechanism failure, in Mozilla's DOM: Security component. CVSS 3.1 is 8.1 with network attack vector, low complexity, no privileges, required user interaction, unchanged scope, high confidentiality impact, high integrity impact, and no availability impact.

Likely exposure

Organizations with Firefox, Firefox ESR, or Thunderbird installations not updated to Mozilla's fixed versions may be exposed. Red Hat references and errata indicate downstream Linux packages may also require vendor-provided updates. Exposure should be assessed across browsers, ESR channels, email clients, and managed desktop images.

Exploitation context

The provided bundle does not show CISA KEV listing or confirmed active exploitation. The CVSS vector indicates exploitation is remote and low complexity, but requires user interaction, consistent with malicious web or message-rendered content risk. No public exploit details should be inferred from these sources.

Researcher notes

Public details are limited to component, weakness class, CVSS, fixed releases, Mozilla advisories, Bugzilla reference, and Red Hat downstream tracking. Do not assume exploitability beyond the CVSS vector. Validation should focus on version and package state rather than reproducing the issue.

Mitigation direction

  • Update Firefox to version 147 or later where applicable.
  • Update Firefox ESR to 115.32 or 140.7 fixed channels.
  • Update Thunderbird to version 147 or 140.7 fixed channels.
  • Apply relevant Red Hat security errata for packaged Mozilla components.
  • Check Mozilla and OS vendor advisories for environment-specific guidance.

Validation and detection

  • Inventory Firefox, Firefox ESR, and Thunderbird versions across managed endpoints.
  • Confirm installed versions match or exceed Mozilla's fixed releases.
  • Check Red Hat systems for applicable RHSA advisories and package status.
  • Review vulnerability scanner findings against CVE-2026-0877 after patching.
  • Verify browser and email client update policies cover ESR channels.
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.

Open ATT&CK lookup
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.

Open ATT&CK lookup
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.

Open CWE intelligenceSame-CWE CVEs