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CVE Record

CVE-2026-2777: Privilege escalation in the Messaging System component

Privilege escalation in the Messaging System component. This vulnerability was fixed in Firefox 148, Firefox ESR 115.33, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8.

CriticalCVSS 9.8Not KEV-listedUpdated
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Glexia's TakeAutomated analysiscritical

Security readout for executives and security teams

Plain-English summary

CVE-2026-2777 is a critical Mozilla privilege-escalation issue in the Messaging System component. The source bundle says it is fixed in Firefox 148, Firefox ESR 115.33, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8. Organizations running older supported channels should treat browser and mail-client updates as urgent.

Executive priority

Prioritize remediation in the next emergency patch window for managed browsers and mail clients. The source bundle does not prove active exploitation, but the critical score and no-user-interaction vector make delayed patching a material endpoint risk.

Technical view

The issue is classified as CWE-269, improper privilege management, with CVSS 3.1 score 9.8 and vector AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. Public details in the bundle are limited; no exploit mechanics are provided. Mozilla and Red Hat references identify fixed releases and downstream advisories.

Likely exposure

Exposure is most likely on endpoints or server images using Mozilla Firefox, Firefox ESR, or Thunderbird versions that have not been updated to the fixed releases named by Mozilla. Red Hat advisories indicate downstream Linux packages may also require vendor updates.

Exploitation context

The bundle does not show CISA KEV listing, and it provides no cited evidence of active exploitation. Risk is still high because the CVSS vector indicates network reachability, low attack complexity, no privileges, no user interaction, and high confidentiality, integrity, and availability impact.

Researcher notes

Public source detail is thin: the bundle names the Messaging System component and CWE-269 but does not describe root cause, trigger path, or exploit preconditions beyond the CVSS vector. Treat validation as version and package-advisory confirmation unless Mozilla publishes deeper technical notes.

Mitigation direction

  • Update Firefox to the fixed channel release identified by Mozilla.
  • Update Firefox ESR to 115.33 or 140.8 as applicable.
  • Update Thunderbird to 148 or 140.8 as applicable.
  • Apply relevant Red Hat security errata for packaged Mozilla builds.
  • Monitor Mozilla and operating-system vendor advisories for revised guidance.

Validation and detection

  • Inventory Firefox, Firefox ESR, and Thunderbird versions across managed endpoints.
  • Confirm installed versions meet or exceed the Mozilla fixed releases.
  • Check Linux package status against applicable Red Hat errata.
  • Review vulnerability scanner results for CVE-2026-2777 after patching.
  • Verify unsupported or unmanaged endpoints are not running affected Mozilla applications.
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 · medium confidence lookup

CWE-269: Authorization and privilege behavior lookup

Authorization weaknesses can support privilege escalation and valid-account review, depending on exploit path. 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-2026-2777 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
Critical
CVSS
9.8 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/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
9.8CVSS 3.1CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H3.95.9CISA-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

9.8Critical
CVSS 3.1 vector shape for CVE-2026-2777Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/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: Privilege escalation in the Messaging System component
other:Red Hat severity ratingcvssV3_1
  • 2026-02-24T14:03:46.784Z: Reported to Red Hat.
  • 2026-02-24T13:33:12.869Z: 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-269

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

CWE-269 · source CWE mapping

Improper Privilege Management

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

Open CWE intelligenceSame-CWE CVEs