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Full vulnerability report · 2026
CVE-2026-74955High confidence

Privilege escalation in the Request Handling component

Mozilla · Firefox

8.8HighCVSS 3.1
Recommended action
Within 7 days

High technical severity; prioritise exposed affected systems while verifying vendor guidance.

Patch available
R
Operational reassessment

Published severity in operational context

Open reassessment dashboard →
Published severityHighOperational priority:High, unchanged from published severity.unchanged

Evidence used

  • No CISA KEV confirmation is currently recorded.
  • EPSS is 0.41% for the current model date.

Compensating controls

  • Validate the affected product branch and deploy the verified fixed release.
  • Restrict the affected network interface to trusted sources where business-safe.
  • Monitor vendor guidance and exploitation sources for a material change.

Verification

  1. Confirm that the asset runs Mozilla Firefox and falls inside the recorded affected range.
  2. Verify the installed build against the product-specific fixed version after deployment.
  3. Validate exposure, authentication requirements and compensating controls in the actual environment.
  4. Reopen this reassessment when CVSS, KEV, EPSS, exploit evidence or remediation changes.
Mitigation target: Within 30 daysRemediation target: Within 180 days

This automated reassessment organises public evidence. It does not know asset exposure, business impact or control effectiveness and does not replace CVSS or a human risk decision.

Distribution package intelligence

Release-specific package status

Debian, ubuntu findings are scoped to the named distribution, release and source package. An absent finding does not mean a package is unaffected.

3 package states
Repository candidate not checked

A published vendor fix does not prove that a matching update is enabled and installable on a particular asset. Confirm the local package candidate before scheduling remediation.

Distribution releaseSource packageVendor stateFixed versionEvidence
Debian sidsid · sourcefirefoxVendor fix publishedDebian records a fixed source-package version for this release.154.0-1Debian Security Tracker ↗Source updated 6 Oct 2026
Ubuntu 24.04 LTSnoble · standard archivemozjs102Under evaluationCanonical reports that the package might be affected and still needs evaluation or fixing.Not published in this feedCanonical Ubuntu Security ↗Source updated 5 Oct 2026
Ubuntu 24.04 LTSnoble · standard archivemozjs115Under evaluationCanonical reports that the package might be affected and still needs evaluation or fixing.Not published in this feedCanonical Ubuntu Security ↗Source updated 5 Oct 2026
Direct vendor intelligence

Authoritative vendor CSAF and VEX advisories

Structured product status and remediation from the issuing vendor. Product-state explanations are always visible; large lists can be searched or downloaded.

1 current
CVE-2026-74955 · CSAF 2.0 · revision 3 · finalRed Hat Product Securityfirefox: thunderbird: Privilege escalation in the Request Handling component
23 known not affected

The vendor explicitly states that these products are not affected by this CVE.

  • firefox as a component of Red Hat Enterprise Linux 10
  • firefox.src as a component of Red Hat Enterprise Linux 10
  • rhel10/firefox-flatpak as a component of Red Hat Enterprise Linux 10
  • rhel10/thunderbird-flatpak as a component of Red Hat Enterprise Linux 10
  • thunderbird as a component of Red Hat Enterprise Linux 10
  • thunderbird.src as a component of Red Hat Enterprise Linux 10
  • firefox as a component of Red Hat Enterprise Linux 6
  • firefox.src as a component of Red Hat Enterprise Linux 6
  • thunderbird as a component of Red Hat Enterprise Linux 6
  • thunderbird.src as a component of Red Hat Enterprise Linux 6
  • firefox as a component of Red Hat Enterprise Linux 7
  • firefox.src as a component of Red Hat Enterprise Linux 7
Summary
A flaw was found in Firefox and Thunderbird. The Mozilla Foundation's Security Advisory describes the following issue: Privilege escalation in the Request Handling component
Remediation
No remediation text is recorded.
Optional official sources

National CERT insights
?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.

Choose official national sources for this report. Each advisory shows its original language. Your selection is remembered on this device and included in shared links.

Official European source

ENISA European Vulnerability Database

Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.

1 current
ENISA EUVD identifier

EUVD-2026-60682

No EUVD known-exploited evidence

Privilege escalation in the Request Handling component. This vulnerability was fixed in Firefox 154, Firefox ESR 153.1, Thunderbird 154, and Thunderbird 153.1.

EUVD state
Present in the current official mapping
Known exploitation
Not present in the current ENISA EUVD known-exploited dataset. This is not proof of no exploitation.
ENISA score
8.8 · CVSS 3.1
Advisory evidence
No linked advisory details stored yet
Recommended actionWithin 7 days

High technical severity; prioritise exposed affected systems while verifying vendor guidance.

Patch available
01

What, why and how

Privilege escalation in the Request Handling component. This vulnerability was fixed in Firefox 154, Firefox ESR 153.1, Thunderbird 154, and Thunderbird 153.1.

What

Privilege escalation in the Request Handling component. This vulnerability was fixed in Firefox 154, Firefox ESR 153.1, Thunderbird 154, and Thunderbird 153.1.

Why

The product does not properly assign, modify, track, or check privileges for an actor, creating an unintended sphere of control for that actor.

How

An attacker operating through a network path may attempt exploitation without authentication after a user interaction. If successful, the issue may gain additional privileges.

What

Privilege escalation in the Request Handling component. This vulnerability was fixed in Firefox 154, Firefox ESR 153.1, Thunderbird 154, and Thunderbird 153.1.

Why

The product does not properly assign, modify, track, or check privileges for an actor, creating an unintended sphere of control for that actor.

How

An attacker operating through a network path may attempt exploitation without authentication after a user interaction. If successful, the issue may gain additional privileges.

02

Exploit reality and attack path

CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.

Observed exploitation
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
No confirmed evidence

No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.

Public PoC / exploit material
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
None recorded

No exploit-tagged reference or CISA SSVC proof-of-concept state is currently recorded. Research may still exist outside the structured feeds.

Likely attack path
a network path → Improper Privilege Management → gain additional privileges
Attack surface
Network
Privileges required
None: unauthenticated exploitation is possible
User interaction
Required interaction required
Attack complexity
Low: no specialised conditions are recorded
Security boundary
Unchanged: impact remains within the vulnerable component's security authority
Weakness
?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-269 ↗

CWE-269: Improper Privilege Management. The product does not properly assign, modify, track, or check privileges for an actor, creating an unintended sphere of control for that actor.

CVSS vector
?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

Common Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.

AVNetworkAttack vector: The vulnerable component can be reached over a network.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.PRNonePrivileges required: The attacker does not need an account or existing privileges.UIRequiredUser interaction: Another user must perform an action for exploitation to succeed.SUnchangedScope: The security impact remains within the vulnerable component's authority.CHighConfidentiality impact: A successful attack can cause a major loss.IHighIntegrity impact: A successful attack can cause a major loss.AHighAvailability impact: A successful attack can cause a major loss.
Post-exploitation / living off the land
No specific living-off-the-land technique is confirmed in the structured sources. Monitor normal administration tools for activity inconsistent with the affected service's baseline.
NetworkUnauthenticatedPrivilege escalationCWE-269
A

Official authority intelligence

Only matched European and national findings are included. Language selectors and unavailable sources are omitted.

ENISA EUVD · EUVD-2026-60682Official EUVD mapping

Privilege escalation in the Request Handling component. This vulnerability was fixed in Firefox 154, Firefox ESR 153.1, Thunderbird 154, and Thunderbird 153.1.

Official EUVD record ↗
BSI · German · WID-SEC-2026-2911Mozilla Firefox, Firefox ESR und Thunderbird: Mehrere Schwachstellen

Ein Angreifer kann mehrere Schwachstellen in Mozilla Firefox, Firefox ESR und Thunderbird ausnutzen, um seine Privilegien zu erhöhen, Sicherheitsmaßnahmen zu umgehen, vertrauliche Informationen offenzulegen, Spoofing- oder Clickjacking-Angriffe durchzuführen oder Denial-of-Service-Zustände herbeizuführen.

Official advisory ↗
CERT-FR · French · CERTFR-2026-AVI-1054Multiples vulnérabilités dans les produits Mozilla

d?id=CVE-2026-74946 Référence CVE CVE-2026-74947 https://www.cve.org/CVERecord?id=CVE-2026-74947 Référence CVE CVE-2026-74948 https://www.cve.org/CVERecord?id=CVE-2026-74948 Référence CVE CVE-2026-74949 https://www.cve.org/CVERecord?id=CVE-2026-74949 Référence CVE CVE-2026-74950 https://www.cve.org/CVERecord?id=CVE-2026-74950 Référence CVE CVE-2026-74951 https://www.cve.org/CVERecord?id=CVE-2026-74951 Référence CVE CVE-2026-74952 https://www.cve.org/CVERecord?id=CVE-2026-74952 Référence CVE CVE-2026-74953 https://www.cve.org/CVERecord?id=CVE-2026-74953 Référence CVE CVE-2026-74954 https://www.cve.org/CVERecord?id=CVE-2026-74954 Référence CVE CVE-2026-74955 https://www.cve.org/CVERecord?id=CVE-2026-74955 Référence CVE CVE-2026-74956 https://www.cve.org/CVERecord?id=CVE-2026-74956 Référence CVE CVE-2026-74957 https://www.cve.org/CVERecord?id=CVE-2026-74957 Référence CVE CVE-2026-74958 https://www.cve.org/CVERecord?id=CVE-2026-74958 Référence CVE CVE-2026-74959 https://www.cve.org/CVERecord?id=CVE-2026-74959 Référence CVE CVE-2026-74960 https://www.cve.org/CVERecord?id=CVE-2026-74960 Référence CVE CVE-2026-74961 https://www.cve.org/CVERecord?id=CVE-2026-74961 Référence CVE CVE-2026-74962 https://www.cve.org/CVERecord?id=CVE-2026-74962 Référence CVE CVE-2026-74963 https://www.cve.org/CVERecord?id=

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2026-028905Mozilla FoundationのMozilla Firefox等の複数製品における権限管理に関する脆弱性

リクエスト処理コンポーネントに存在する権限昇格の脆弱性です。この脆弱性はFirefox 154、Firefox ESR 153.1、Thunderbird 154、およびThunderbird 153.1で修正されました。

Official advisory ↗
03

Patch and workaround

Operational remediation based on structured source evidence.

Status
?Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.
Patch available
Affected
See the vendor and CVE records for the affected range.
Fixed
Action
Review the linked authoritative reference and apply the recorded fixed release appropriate to the affected product branch.
Workaround
No verified workaround is recorded. If business-safe, reduce exposure to the affected interface and allow only trusted sources until authoritative guidance is available.
Official vendor articles8 stored documents

Linked articles are downloaded and versioned as source evidence. A CVE mention or approved update relationship does not, by itself, verify a fix for every product branch.

  • Security Vulnerabilities fixed in Firefox 154 — Mozilla →Original publisher ↗Searchable text snapshot · Captured 27 Sep 2026Security Vulnerabilities fixed in Firefox 154 Announced August 18, 2026 Impact high Products Firefox Fixed in Firefox 154 # CVE-2026-75874: Sandbox escape in the Remote Settings Client component Reporter crixer Impact high References Bug 2039972 # CVE-2026-74934: Site isolation issue in the Graphics: Canva
  • Security Vulnerabilities fixed in Firefox ESR 153.1 — Mozilla →Original publisher ↗Searchable text snapshot · Captured 27 Sep 2026Security Vulnerabilities fixed in Firefox ESR 153.1 Announced August 18, 2026 Impact high Products Firefox ESR Fixed in Firefox ESR 153.1 # CVE-2026-74934: Site isolation issue in the Graphics: CanvasWebGL component Reporter satyamasd Impact high References Bug 2050584 # CVE-2026-74935: Privilege escalatio
  • Security Vulnerabilities fixed in Thunderbird 154 — Mozilla →Original publisher ↗Searchable text snapshot · Captured 27 Sep 2026Security Vulnerabilities fixed in Thunderbird 154 Announced August 18, 2026 Impact high Products Thunderbird Fixed in Thunderbird 154 In general, these flaws cannot be exploited through email in the Thunderbird product because scripting is disabled when reading mail, but are potentially risks in browser or brows
  • Security Vulnerabilities fixed in Thunderbird 153.1 — Mozilla →Original publisher ↗Searchable text snapshot · Captured 27 Sep 2026Security Vulnerabilities fixed in Thunderbird 153.1 Announced August 18, 2026 Impact high Products Thunderbird Fixed in Thunderbird 153.1 In general, these flaws cannot be exploited through email in the Thunderbird product because scripting is disabled when reading mail, but are potentially risks in browser or b
  • Security Vulnerabilities fixed in Firefox 154 — Mozilla →Original publisher ↗Searchable text snapshot · Captured 27 Sep 2026Security Vulnerabilities fixed in Firefox 154 Announced August 18, 2026 Impact high Products Firefox Fixed in Firefox 154 # CVE-2026-75874: Sandbox escape in the Remote Settings Client component Reporter crixer Impact high References Bug 2039972 # CVE-2026-74934: Site isolation issue in the Graphics: Canva
  • Security Vulnerabilities fixed in Firefox ESR 153.1 — Mozilla →Original publisher ↗Searchable text snapshot · Captured 27 Sep 2026Security Vulnerabilities fixed in Firefox ESR 153.1 Announced August 18, 2026 Impact high Products Firefox ESR Fixed in Firefox ESR 153.1 # CVE-2026-74934: Site isolation issue in the Graphics: CanvasWebGL component Reporter satyamasd Impact high References Bug 2050584 # CVE-2026-74935: Privilege escalatio
  • Security Vulnerabilities fixed in Thunderbird 153.1 — Mozilla →Original publisher ↗Searchable text snapshot · Captured 27 Sep 2026Security Vulnerabilities fixed in Thunderbird 153.1 Announced August 18, 2026 Impact high Products Thunderbird Fixed in Thunderbird 153.1 In general, these flaws cannot be exploited through email in the Thunderbird product because scripting is disabled when reading mail, but are potentially risks in browser or b
  • Security Vulnerabilities fixed in Thunderbird 154 — Mozilla →Original publisher ↗Searchable text snapshot · Captured 26 Sep 2026Security Vulnerabilities fixed in Thunderbird 154 Announced August 18, 2026 Impact high Products Thunderbird Fixed in Thunderbird 154 In general, these flaws cannot be exploited through email in the Thunderbird product because scripting is disabled when reading mail, but are potentially risks in browser or brows
04

Evidence and provenance

Published 18 Aug 2026 · Last source change 21 Aug 2026, 03:55 UTC · CWE-269 · Improper Privilege Management

CVE recordCVE.org · 5.2
CVSS sourceCISA ADP
EPSS source
?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.
FIRST · tracked since 2026-08-23
European sourceENISA EUVD · EUVD-2026-60682
Product sourceCNA
Remediation sourceCVE/CNA references
CWE sourceCISA ADP
NVD statusNVD enriched

Missing structured fields: affected versions. Missing data is not evidence of low risk; review the primary advisory.

Material change intelligence

What changed after publication

View recent updates ↗
  1. Vendor guidanceAuthoritative vendor guidance changed: added vendor advisory: mozilla.org/mfsa2026-74; added vendor advisory: mozilla.org/mfsa2026-77; 2 further additions.
    Before
    remediation: bugzilla.mozilla.org/show_bug.cgi?id=2029265
    After
    remediation: bugzilla.mozilla.org/show_bug.cgi?id=2029265 · vendor advisory: mozilla.org/mfsa2026-74 · vendor advisory: mozilla.org/mfsa2026-77 · 2 more references
    security@mozilla.org ↗
  2. Vendor guidanceAuthoritative vendor guidance changed: added remediation: bugzilla.mozilla.org/show_bug.cgi?id=2029265; removed remediation: mozilla.org/mfsa2026-78.
    Before
    remediation: mozilla.org/mfsa2026-78
    After
    remediation: bugzilla.mozilla.org/show_bug.cgi?id=2029265
    CNA ↗
  3. Vendor guidanceAuthoritative vendor guidance changed: added remediation: mozilla.org/mfsa2026-78; removed remediation: bugzilla.mozilla.org/show_bug.cgi?id=2029265.
    Before
    remediation: bugzilla.mozilla.org/show_bug.cgi?id=2029265
    After
    remediation: mozilla.org/mfsa2026-78
    CNA ↗
  4. SeveritySeverity changed from Unknown to High.
    Before
    Unknown
    After
    High
    CISA ADP ↗
  5. CVSS scoreCVSS score changed from not recorded to 8.8 (CVSS 3.1 · CISA ADP · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H).
    Before
    not recorded
    After
    8.8 (CVSS 3.1 · CISA ADP · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H)
    CISA ADP ↗
  6. Catalogue recordCVE added to the BlackTree catalogue.
    CNA ↗
Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
Fixed release or patch reference recorded
ENISA EUVD · EUVD-2026-60682↗Vendor CSAF · Red Hat Product Security↗Vendor advisory↗Vendor advisory↗Vendor advisory↗Vendor advisory↗CVE authority or vendor reference↗Official CVE record (CNA and ADP data)↗NVD record↗
Technical terms and abbreviations used in this report
CVE
Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS
Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS
Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE
Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA
CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP
Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD
National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT
A computer security incident response team that publishes warnings or coordinates incident response.
PoC
Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF
Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL
Living off the land: abuse of legitimate tools or system functions during an attack.
Free version - for non-commercial use only.CVE-2026-74955 · cve.blacktree.nl