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CVE Record

CVE-2026-16396: Privilege escalation in WebExtensions

Privilege escalation in WebExtensions. This vulnerability was fixed in Firefox 153, Firefox ESR 140.13, Thunderbird 153, and Thunderbird 140.13.

HighCVSS 8.8Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

A flaw in Mozilla WebExtensions could allow an attacker to gain elevated privileges after user interaction, potentially compromising data, system actions, and availability. Mozilla fixed it in current Firefox and Thunderbird releases. Organizations should quickly identify and update older installations.

Executive priority

Treat this as an accelerated patching priority because exploitation could have broad security impact and requires no existing attacker privileges. Focus first on internet-using endpoints with older Firefox or Thunderbird installations, while avoiding claims of an active campaign.

Technical view

CVE-2026-16396 is a WebExtensions privilege-escalation vulnerability categorized as CWE-269. Its CVSS 3.1 score is 8.8: network-accessible, low complexity, no prior privileges, and user interaction required, with potentially high confidentiality, integrity, and availability impact.

Likely exposure

Potential exposure includes Firefox and Thunderbird installations preceding the stated fixed releases. The bundle does not provide exact lower version boundaries or required WebExtension conditions, so organizations should compare deployed versions with Mozilla's applicable advisory.

Exploitation context

The source bundle reports no CISA KEV listing and provides no evidence of active exploitation. This does not establish that exploitation has never occurred. User interaction is required according to the CVSS vector, but the triggering interaction is not described.

Researcher notes

The structured affected list repeats versions 140.13 and 153, while the description identifies them as fixed releases. Treat them as remediation thresholds, not confirmed vulnerable versions. The bundle omits the faulty privilege boundary, triggering sequence, affected lower bounds, indicators, and exploit evidence.

Mitigation direction

  • Upgrade to Firefox 153 or Firefox ESR 140.13, and Thunderbird 153 or Thunderbird 140.13, as applicable.
  • Prioritize managed endpoints still running releases below the applicable fixed version.
  • Verify automatic-update and enterprise deployment policies are successfully delivering current Mozilla releases.
  • If upgrades are delayed, consult Mozilla's applicable advisory; the provided bundle names no alternative mitigation.

Validation and detection

  • Inventory Firefox and Thunderbird versions across endpoints and supported release channels.
  • Confirm Firefox 153, Firefox ESR 140.13, Thunderbird 153, Thunderbird 140.13, or later is installed, as applicable.
  • Re-scan managed endpoints after deployment to identify update failures or unmanaged installations.
  • Document exceptions and compare them against current Mozilla advisory guidance.
  • Do not rely on alert absence; the bundle supplies no indicators of compromise or detection signatures.
Prepared
Confidence
medium
Sources
7

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-2026-16396 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
High
CVSS
8.8 (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: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.

1CVSS vectors
3Timeline events
1ADP providers
6Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: noTechnical Impact: total

CVSS vector scores

1 official score

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
8.8CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H2.85.9CISA-ADP

Vulnerability scoring details

Base CVSS 3.1 score

8.8High
CVSS 3.1 vector shape for CVE-2026-16396Attack 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: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. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
cvssV3_1other:ssvc

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
MozillaFirefox140.13, 153Listed
MozillaThunderbird140.13, 153Listed
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