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CVE Record

CVE-2026-2776: Sandbox escape due to incorrect boundary conditions in the Telemetry component in External Software

Sandbox escape due to incorrect boundary conditions in the Telemetry component in External Software. 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

This is a critical Mozilla sandbox escape. A flaw in Telemetry boundary handling could let an attacker break out of intended isolation, threatening 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

Treat this as an immediate patch-management priority for Mozilla browser and mail-client estates. There is no supplied evidence of active exploitation, but the critical score and sandbox-escape impact justify rapid remediation and exception tracking.

Technical view

CVE-2026-2776 is described as incorrect boundary conditions in the Telemetry component in External Software, 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.

Likely exposure

Organizations using Firefox or Thunderbird before the listed fixed releases should treat exposure as urgent. Red Hat also tracks this CVE and multiple RHSA advisories, so Linux package consumers should validate vendor package status rather than relying only on upstream version numbers.

Exploitation context

The supplied sources do not show CISA KEV listing or confirmed active exploitation. The risk is still high because the CVSS vector indicates remote, unauthenticated exploitation without user interaction and full impact after sandbox escape.

Researcher notes

The public description is sparse and Bugzilla details may be restricted. Avoid assuming a specific exploit primitive beyond CWE-119 and boundary-condition failure. Validate exposure through installed versions and vendor advisories, not proof-of-concept behavior.

Mitigation direction

  • Update Firefox to Mozilla’s fixed release line listed for your deployment.
  • Update Thunderbird to Mozilla’s fixed release line listed for your deployment.
  • Apply relevant Red Hat security advisories where Red Hat packages are used.
  • Check Mozilla and OS vendor guidance for any product-specific mitigation details.
  • Prioritize managed endpoints, VDI images, and servers with browser or mail clients installed.

Validation and detection

  • Inventory Firefox and Thunderbird versions across endpoints and server images.
  • Confirm Firefox is at 148, ESR 115.33, ESR 140.8, or later applicable builds.
  • Confirm Thunderbird is at 148, 140.8, or later applicable builds.
  • Review Red Hat errata applicability for installed Mozilla-related packages.
  • Document exceptions where fixed packages are unavailable and monitor vendor updates.
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

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-2026-2776 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-2026-2776Attack 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 Telemetry component in External Software
other:Red Hat severity ratingcvssV3_1
  • 2026-02-24T14:02:24.297Z: Reported to Red Hat.
  • 2026-02-24T13:33:12.247Z: 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