Security Resilience

CVE-2026-4689

Memory Safety in Mozilla Firefox ≤ 115.34.0

Memory Safety
Published
24 March 2026
Modified
15 July 2026
Patch / advisory
View advisory
CVSS Score v3.1 10.0
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
EPSS Score 0.0066 51th percentile
Risk Priority 75 floored blend · peak EPSS

CVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.

Summary

CVE-2026-4689 is a critical-severity Integer Overflow or Wraparound (CWE-190) vulnerability in Mozilla Firefox. Its CVSS base score is 10.0 (Critical).

Operationally, exploitation aligns with the MITRE ATT&CK technique NTDS (T1003.003); ranked in the top 49% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog.

The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and SI-10 (Information Input Validation) — 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-2026-4689 is a sandbox escape vulnerability stemming from incorrect boundary conditions and an integer overflow in the XPCOM component of Mozilla products. It affects Firefox versions prior to 149, Firefox ESR versions prior to 115.34 and 140.9, Thunderbird versions prior to 149, and Thunderbird versions prior to 140.9. The issue is classified under CWE-190 (Integer Overflow or Wraparound), CWE-754 (Improper Check for Unusual or Exceptional Conditions), and CWE-120 (Buffer Copy without Checking Size of Input), with a CVSS v3.1 base score of 10.0 (AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H), indicating critical severity due to its potential for complete system compromise.

A remote attacker can exploit this vulnerability over the network with low complexity, requiring no privileges, authentication, or user interaction. Successful exploitation allows scope change from the sandboxed browser process to the host system, granting high-impact confidentiality, integrity, and availability violations, such as arbitrary code execution with the privileges of the affected application.

Mozilla's security advisories (MFSA 2026-20 through 2026-23) and the associated Bugzilla entry (bug 2016374) detail the patch, recommending immediate updates to Firefox 149, Firefox ESR 115.34 or 140.9, Thunderbird 149, or Thunderbird 140.9 to mitigate the issue. No workarounds are specified beyond applying these fixed releases.

OWASP Top 10 for Web (2025)

A10:2025 Mishandling of Exceptional Conditions

EU & UK References

Vulnerability Data

Sandbox escape due to incorrect boundary conditions, integer overflow in the XPCOM component. This vulnerability was fixed in Firefox 149, Firefox ESR 115.34, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.

CWE(s)
CWE-190CWE-754CWE-120

Related Threats

MITRE ATT&CK Enterprise Techniques

T1003.003 NTDS Credential Access
Adversaries may attempt to access or create a copy of the Active Directory domain database in order to steal credential information, as well as obtain other information about domain members such as devices, users, and access rights.
attack.mitre.org →
T1003.004 LSA Secrets Credential Access
Adversaries with SYSTEM access to a host may attempt to access Local Security Authority (LSA) secrets, which can contain a variety of different credential materials, such as credentials for service accounts.
attack.mitre.org →
T1003.005 Cached Domain Credentials Credential Access
Adversaries may attempt to access cached domain credentials used to allow authentication to occur in the event a domain controller is unavailable.
attack.mitre.org →
T1003.006 DCSync Credential Access
Adversaries may attempt to access credentials and other sensitive information by abusing a Windows Domain Controller's application programming interface (API)(Citation: Microsoft DRSR Dec 2017) (Citation: Microsoft GetNCCChanges) (Citati…
attack.mitre.org →
T1003.008 /etc/passwd and /etc/shadow Credential Access
Adversaries may attempt to dump the contents of <code>/etc/passwd</code> and <code>/etc/shadow</code> to enable offline password cracking.
attack.mitre.org →
T1006 Direct Volume Access Stealth
Adversaries may directly access a volume to bypass file access controls and file system monitoring.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2026-4694Same product: Mozilla Firefox
CVE-2026-4690Same product: Mozilla Firefox
CVE-2026-0880Same product: Mozilla Firefox
CVE-2026-16402Same product: Mozilla Firefox
CVE-2026-16389Same product: Mozilla Firefox
CVE-2026-8956Same product: Mozilla Firefox
CVE-2025-10533Same product: Mozilla Firefox
CVE-2026-2762Same product: Mozilla Firefox
CVE-2026-6773Same product: Mozilla Firefox
CVE-2026-6783Same product: Mozilla Firefox

Affected Assets

mozilla
firefox
≤ 115.34.0 · ≤ 149.0 · 128.0 — 140.9.0
mozilla
thunderbird
≤ 140.9.0 · ≤ 149.0

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)

—

Validate
Prove the fix (OWASP ASVS)
  • V5.2.1
  • V5.2.6

Mitigating Controls (NIST 800-53 r5) AI

SA-11 Developer Testing and Evaluation good match

Developer testing and evaluation (static analysis, fuzzing, unit tests) directly finds integer overflow defects before deployment.

SI-10 Information Input Validation good match

Input validation directly requires checking for unexpected or malformed conditions before they propagate.

SA-8 Security and Privacy Engineering Principles partial match

Secure engineering principles require use of safe arithmetic constructs or language features that structurally eliminate integer overflow during calculation.

SI-16 Memory Protection partial match

Memory protection limits the impact of an overflow once it occurs.

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.

ID.RA-01 partial match
blocks

Vulnerability identification processes such as code review or scanning detect classic buffer overflows before exploitation.

PR.PS-02 partial match
blocks

Routine patching replaces vulnerable code containing unchecked buffer copies with corrected versions.

PR.PS-06 partial match
blocks

Secure SDLC practices directly require use of safe arithmetic, bounds checks, and testing that prevent integer overflows.

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.5.14 Information transfer partial match
removes
A.5.15 Access control partial match
removes
A.5.16 Identity management partial match
removes
A.5.17 Authentication information partial match
removes
A.5.18 Access rights partial match
removes
A.8.10 Information deletion partial match
removes

Hardening callouts derived

DISA STIG baselines are authored against specific weaknesses. Where this CVE cites a broad weakness class, the mapping is not asserted at that abstraction (owner ruling, 2026-09-25: grade only at Base and below), so no rule is shown here rather than a rule shown against the wrong grain.

  • No fine-grained STIG row for CWE-754, a class-level weakness. Rules are authored against its narrower children: CWE-354.

References