Cyber Resilience

CVE-2026-0877

Mozilla Firefox ≤ 115.32.0

Published
13 January 2026
Modified
15 July 2026
Patch / advisory
View advisory
CVSS Score v3.1 8.1
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N
EPSS Score 0.0043 35th percentile
Risk Priority 60 floored blend · peak EPSS

Summary

CVE-2026-0877 is a high-severity Protection Mechanism Failure (CWE-693) vulnerability in Mozilla Firefox. Its CVSS base score is 8.1 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Abuse Elevation Control Mechanism (T1548); ranked at the 35th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

The strongest mitigations our analysis identified map to AC-3 (Access Enforcement) and AC-4 (Information Flow Enforcement) — see the control section below for these in your framework.

Deeper analysis AI-assisted summary

Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.

CVE-2026-0877 is a mitigation bypass vulnerability in the DOM: Security component of Mozilla Firefox and Thunderbird. It affects versions of Firefox prior to 147, Firefox ESR prior to 115.32 and 140.7, Thunderbird prior to 147, and Thunderbird prior to 140.7. The issue, classified under CWE-693 (Protection Mechanism Failure), was published on 2026-01-13 and carries a CVSS v3.1 base score of 8.1 (AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N), indicating high severity due to its potential for confidentially and integrity impacts.

A remote attacker can exploit this vulnerability without privileges by tricking a user into interacting with malicious content, such as visiting a crafted webpage. Successful exploitation bypasses security mitigations in the DOM, enabling high-impact confidentiality violations like information disclosure and integrity violations such as content manipulation, while maintaining unchanged scope and no availability disruption.

Mozilla's security advisories (MFSA 2026-01 through 2026-04) and the associated Bugzilla entry (1999257) confirm the vulnerability was addressed by updating to Firefox 147, Firefox ESR 115.32 or 140.7, Thunderbird 147, or Thunderbird 140.7, recommending immediate patching for affected users.

OWASP Top 10 for Web (2025)

A06:2025 Insecure Design

EU & UK References

Vulnerability Data

Mitigation bypass in the DOM: Security component. This vulnerability was fixed in Firefox 147, Firefox ESR 115.32, Firefox ESR 140.7, Thunderbird 147, and Thunderbird 140.7.

CWE(s)
CWE-693

Related Threats

MITRE ATT&CK Enterprise Techniques

T1548 Abuse Elevation Control Mechanism Privilege Escalation
Adversaries may circumvent mechanisms designed to control privilege elevation to gain higher-level permissions.
attack.mitre.org →
T1553 Subvert Trust Controls Defense Impairment
Adversaries may undermine security controls that will either warn users of untrusted activity or prevent execution of untrusted programs.
attack.mitre.org →
T1553.005 Mark-of-the-Web Bypass Defense Impairment
Adversaries may abuse specific file formats to subvert Mark-of-the-Web (MOTW) controls.
attack.mitre.org →
T1600 Weaken Encryption Defense Impairment
Adversaries may compromise a network device’s encryption capability in order to bypass encryption that would otherwise protect data communications.
attack.mitre.org →
T1689 Downgrade Attack Defense Impairment
Adversaries may downgrade or use a version of system features that may be outdated, vulnerable, and/or does not support updated security controls.
attack.mitre.org →
T1040 Network Sniffing Credential Access
Adversaries may passively sniff network traffic to capture information about an environment, including authentication material passed over the network.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2026-6763Same product: Mozilla Firefox
CVE-2025-10528Same product: Mozilla Firefox
CVE-2026-16377Same product: Mozilla Firefox
CVE-2026-16370Same product: Mozilla Firefox
CVE-2026-16383Same product: Mozilla Firefox
CVE-2026-6774Same product: Mozilla Firefox
CVE-2026-12316Same product: Mozilla Firefox
CVE-2026-16390Same product: Mozilla Firefox
CVE-2026-16388Same product: Mozilla Firefox
CVE-2026-2761Same product: Mozilla Firefox

Affected Assets

mozilla
firefox
≤ 115.32.0 · ≤ 147.0 · 128.0 — 140.7.0
mozilla
thunderbird
≤ 140.7.0 · ≤ 147.0

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)
  • 8 hardening rules · 6 OS baselines
Validate
Prove the fix (OWASP ASVS)
  • V6.3.3
  • V6.6.3
  • V10.2.2

Mitigating Controls (NIST 800-53 r5) AI

AC-3 Access Enforcement good match

AC-3 directly requires enforcement of access authorizations via the protection mechanism itself.

AC-4 Information Flow Enforcement good match

AC-4 mandates use of information flow enforcement mechanisms to control data movement.

SC-2 Separation of System and User Functionality good match

SC-2 requires separation of user and system functionality as a protection mechanism.

SC-28 Protection of Information at Rest good match

SC-28 requires protection mechanisms for information at rest.

SC-3 Security Function Isolation good match

SC-3 requires isolation of security functions from non-security functions.

SC-7 Boundary Protection good match

SC-7 requires boundary protection mechanisms to monitor and control external communications.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.AA-03 mostly match
prevents

Enforcing authentication directly implements a core protection mechanism whose absence or misuse is the CWE.

PR.AA-05 mostly match
prevents

Defining and enforcing access authorizations is a protection mechanism; proper use prevents the CWE.

PR.DS-01 mostly match
prevents

Cryptographic and integrity controls are protection mechanisms whose correct deployment mitigates the CWE.

PR.DS-02 mostly match
prevents

Encryption and integrity protections for transit are explicit protection mechanisms.

PR.IR-01 mostly match
prevents

Logical network protections are protection mechanisms whose failure matches the CWE.

PR.PS-01 partial match
prevents

Hardened configuration baselines ensure protection mechanisms are correctly applied and maintained.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.5.36 Compliance with policies, rules and standards for information security partial match
finds

Systematic verification that security mechanisms operate according to defined standards reduces the likelihood that protection mechanisms are bypassed or disabled.

A.8.20 Networks security partial match
mitigates

Hardening devices, disabling vulnerable protocols, and maintaining accurate network diagrams reduce the likelihood that a protection mechanism is misconfigured or left in a weak state.

A.5.24 Information security incident management planning and preparation none match
none

Requiring defined escalation paths, crisis activation criteria, and coordination procedures strengthens the overall protection mechanism so that a single control failure is less likely to leave the organization exposed.

A.5.25 Assessment and decision on information security events none match
none

By requiring a documented categorization and decision process for security events, the control ensures that protection mechanisms are not bypassed or ignored when anomalies occur.

A.5.26 Response to information security incidents none match
none

Identifying and remediating control weaknesses that contributed to an incident reduces the likelihood that protection mechanisms will fail again.

A.5.27 Learning from information security incidents none match
none

Post-incident analysis that feeds updated risk assessments and additional controls directly reduces the chance that previously exploited weaknesses will recur.

Hardening callouts derived

Configuration rules from DISA STIG baselines that bear on weaknesses of the type cited by this CVE. Each rule is shown with the relationship its mapping actually records, against the CWE it was authored against. Derived via CVE→CWE over `controls_xwalks` (authoritative rows only; rows rated `none` are excluded).

Oracle Linux 8 (2 rules)
  • V-248524 OL 8 must implement NIST FIPS-validated cryptography for the following: To provision digital signatures, to generate cryptographic hashes, and to protect data requiring data-at-rest protections in accordance with applicable federal laws, Executive Orders, directives, policies, regulations, and standards. prevents CWE-693
  • V-248525 All OL 8 local disk partitions must implement cryptographic mechanisms to prevent unauthorized disclosure or modification of all information that requires at-rest protection. prevents CWE-693
Windows 10 (2 rules)
  • V-220865 The Windows Remote Management (WinRM) service must not use Basic authentication. prevents CWE-693
  • V-220812 Credential Guard must be running on Windows 10 domain-joined systems. prevents CWE-693
Windows 11 (1 rule)
  • V-253418 The Windows Remote Management (WinRM) service must not use Basic authentication. prevents CWE-693
Windows Server 2016 (1 rule)
  • V-225012 Windows Server 2016 must be running Credential Guard on domain-joined member servers. prevents CWE-693
Windows Server 2019 (1 rule)
  • V-205907 Windows Server 2019 must be running Credential Guard on domain-joined member servers. prevents CWE-693
Windows Server 2022 (1 rule)
  • V-254441 Windows Server 2022 must be running Credential Guard on domain-joined member servers. prevents CWE-693

References