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CVE Record

CVE-2026-0878: Sandbox escape due to incorrect boundary conditions in the Graphics: CanvasWebGL component

Sandbox escape due to incorrect boundary conditions in the Graphics: CanvasWebGL component. This vulnerability was fixed in Firefox 147, Firefox ESR 140.7, Thunderbird 147, and Thunderbird 140.7.

HighCVSS 8Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

CVE-2026-0878 is a high-severity Mozilla sandbox escape in the CanvasWebGL graphics component. A successful attack could let malicious content cross a browser or mail-client security boundary, risking sensitive data and system integrity. Mozilla states it is fixed in Firefox 147, Firefox ESR 140.7, Thunderbird 147, and Thunderbird 140.7.

Executive priority

Patch on a normal emergency browser cadence: high priority, especially for user workstations and mail clients. There is no provided evidence of active exploitation, but sandbox escapes can materially increase impact when paired with other flaws.

Technical view

The CVSS 3.1 vector is 8.0 high: network reachable, no privileges, user interaction required, high attack complexity, changed scope, high confidentiality and integrity impact. The assigned weaknesses are CWE-119 and CWE-20, indicating memory/boundary and input validation issues in Graphics: CanvasWebGL.

Likely exposure

Exposure is most likely where Firefox or Thunderbird versions earlier than the fixed releases remain deployed, including enterprise Linux distributions tracking Mozilla packages. The bundle also cites Red Hat CVE, VEX, and errata sources, indicating downstream package handling exists.

Exploitation context

The provided bundle does not show CISA KEV listing or any cited evidence of active exploitation. The CVSS vector indicates exploitation requires user interaction and high attack complexity, but no privileges. Treat public browsing and email-client use as meaningful exposure until patched.

Researcher notes

Evidence is limited to advisory-level detail. The Bugzilla reference is cited, but the bundle does not provide technical reproduction detail. Avoid assuming exploitability beyond the CVSS vector and Mozilla’s description. Focus validation on fixed-version confirmation and downstream vendor status.

Mitigation direction

  • Update Firefox to version 147 or Firefox ESR 140.7 or later.
  • Update Thunderbird to version 147 or 140.7 or later.
  • Review Mozilla and Red Hat advisories for environment-specific package guidance.
  • Prioritize managed endpoints that browse untrusted web content or process external mail.
  • If patching is delayed, check vendor guidance for supported temporary risk reduction.

Validation and detection

  • Inventory installed Firefox and Thunderbird versions across endpoints and servers.
  • Confirm deployed versions meet or exceed Mozilla’s fixed releases.
  • Check Linux package status against relevant Red Hat advisories where applicable.
  • Verify vulnerability scanners map detections to CVE-2026-0878, not only product names.
  • Document exceptions where vendor guidance shows a package is not affected.
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.

Open ATT&CK lookup
cwe · low confidence lookup

CWE-20: 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
description · low confidence lookup

Privilege behavior lookup

The CVE wording references privilege impact, so privilege escalation and authorization behavior review may help. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.

Open ATT&CK lookup
cve · low confidence lookup

CVE-2026-0878 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 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/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
32Source 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
8CVSS 3.1HighCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:H/A:N1.65.8CISA-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

8High
CVSS 3.1 vector shape for CVE-2026-0878Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/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: Sandbox escape due to incorrect boundary conditions in the Graphics: CanvasWebGL component
other:Red Hat severity ratingcvssV3_1
  • 2026-01-13T14:01:34.680Z: Reported to Red Hat.
  • 2026-01-13T13:30:53.697Z: 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-119CWE-20

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.

Open CWE intelligenceSame-CWE CVEs
CWE-20 · source CWE mapping

Improper Input Validation

Improper Input Validation represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs