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CVE Record

CVE-2026-2778: Sandbox escape due to incorrect boundary conditions in the DOM: Core & HTML component

Sandbox escape due to incorrect boundary conditions in the DOM: Core & HTML component. This vulnerability was fixed in Firefox 148, Firefox ESR 115.33, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8.

CriticalCVSS 10Not KEV-listedUpdated
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Glexia's TakeAutomated analysiscritical

Security readout for executives and security teams

Plain-English summary

CVE-2026-2778 is a critical Mozilla sandbox escape in DOM Core and HTML handling. A successful attack could break browser or mail-client isolation and affect confidentiality, integrity, and availability. Mozilla says it was fixed in Firefox 148, Firefox ESR 115.33 and 140.8, Thunderbird 148, and Thunderbird 140.8.

Executive priority

Handle as an emergency browser and mail-client patching item. No active exploitation is proven in the provided sources, but the impact rating and sandbox-escape nature justify rapid inventory, update deployment, and exception tracking.

Technical view

The source describes incorrect boundary conditions in Mozilla DOM Core and HTML components, mapped to CWE-119. The CVSS 3.1 score is 10.0 with network attack vector, low complexity, no privileges, no user interaction, changed scope, and high CIA impact. Public details are limited; do not infer a reliable exploit path from the available bundle.

Likely exposure

Exposure is most likely where Firefox or Thunderbird is below the fixed Mozilla releases, or where downstream vendor packages have not received their security errata. Red Hat advisories indicate packaged ecosystem impact, but the bundle does not enumerate every affected distribution package.

Exploitation context

The bundle marks CISA KEV as false and provides no cited evidence of active exploitation. Treat it as urgent because of the CVSS 10.0 rating and sandbox-escape class, not because active exploitation is confirmed here.

Researcher notes

The bundle gives limited root-cause detail beyond incorrect DOM boundary conditions and CWE-119. The listed product versions appear to be fixed releases, so avoid treating them as vulnerable without vendor clarification. Bugzilla and Mozilla advisories should be reviewed for any disclosed technical constraints.

Mitigation direction

  • Upgrade Firefox to 148, ESR 115.33, ESR 140.8, or later vendor-fixed builds.
  • Upgrade Thunderbird to 148, 140.8, or later vendor-fixed builds.
  • Apply applicable Red Hat security errata for managed Linux systems.
  • Check Mozilla and OS vendor guidance for environment-specific fixes.
  • Prioritize systems used for web browsing, email, and privileged administration.

Validation and detection

  • Inventory installed Firefox and Thunderbird versions across endpoints and servers.
  • Compare versions against Mozilla fixed releases listed in the CVE bundle.
  • Check Linux package status against applicable Red Hat errata or vendor advisories.
  • Confirm security update deployment through endpoint management or package audit records.
  • Review exposure for systems where browser or mail content is processed automatically.
Prepared
Confidence
medium
Sources
11

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

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.

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cve · low confidence lookup

CVE-2026-2778 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
Critical
CVSS
10 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/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
35Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: yesTechnical 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
10CVSS 3.1CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H3.96CISA-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

10Critical
CVSS 3.1 vector shape for CVE-2026-2778Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/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: Sandbox escape due to incorrect boundary conditions in the DOM: Core & HTML component
other:Red Hat severity ratingcvssV3_1
  • 2026-02-24T14:05:18.491Z: Reported to Red Hat.
  • 2026-02-24T13:33:13.564Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
MozillaFirefox115.33, 140.8, 148Listed
MozillaThunderbird140.8, 148Listed
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.

Open CWE intelligenceSame-CWE CVEs