Security Resilience

CVE-2026-6777

DoS in Mozilla Firefox ≤ 150.0

DoSCSRF
Published
21 April 2026
Modified
22 April 2026
Patch / advisory
View advisory
CVSS Score v3.1 5.3
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
EPSS Score 0.0023 12th percentile
Risk Priority 43 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-2026-6777 is a medium-severity Improper Input Validation (CWE-20) vulnerability in Mozilla Firefox. Its CVSS base score is 5.3 (Medium).

Operationally, exploitation aligns with the MITRE ATT&CK technique Security Account Manager (T1003.002); ranked at the 12th 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 SA-11 (Developer Testing and Evaluation) and SC-5 (Denial-of-service Protection) — 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-2026-6777 is an unspecified vulnerability classified as "other issue" in the Networking: DNS component of Mozilla Firefox and Thunderbird. The flaw, associated with CWE-20 (Improper Input Validation), CWE-352 (Cross-Site Request Forgery), and CWE-400 (Uncontrolled Resource Consumption), carries a CVSS v3.1 base score of 5.3 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L), indicating medium severity with primary impact on availability.

Remote attackers can exploit this vulnerability over the network without authentication or user interaction, requiring low attack complexity. Successful exploitation results in a low-impact denial of service, such as resource exhaustion or service disruption, but does not compromise confidentiality or integrity.

Mozilla's security advisories (MFSA 2026-30 and MFSA 2026-33) and the associated Bugzilla entry (bug 2022726) confirm the issue was addressed in Firefox version 150 and Thunderbird version 150. Security practitioners should ensure affected users upgrade to these patched versions to mitigate the risk.

OWASP Top 10 for Web (2025)

A01:2025 Broken Access ControlA05:2025 Injection

EU & UK References

Vulnerability Data

Other issue in the Networking: DNS component. This vulnerability was fixed in Firefox 150 and Thunderbird 150.

CWE(s)
CWE-20CWE-352CWE-400

Related Threats

MITRE ATT&CK Enterprise Techniques

T1003.002 Security Account Manager Credential Access
Adversaries may attempt to extract credential material from the Security Account Manager (SAM) database either through in-memory techniques or through the Windows Registry where the SAM database is stored.
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 →
T1003.007 Proc Filesystem Credential Access
Adversaries may gather credentials from the proc filesystem or `/proc`.
attack.mitre.org →
T1005 Data from Local System Collection
Adversaries may search local system sources, such as file systems, configuration files, local databases, virtual machine files, or process memory, to find files of interest and sensitive data prior to Exfiltration.
attack.mitre.org →
T1012 Query Registry Discovery
Adversaries may interact with the Windows Registry to gather information about the system, configuration, and installed software.
attack.mitre.org →
T1016.002 Wi-Fi Discovery Discovery
Adversaries may search for information about Wi-Fi networks, such as network names and passwords, on compromised systems.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2025-4088Same product: Mozilla Firefox
CVE-2023-4047Same product: Mozilla Firefox
CVE-2023-28173Shared CWE-352
CVE-2023-51668Shared CWE-352
CVE-2023-32500Shared CWE-352
CVE-2023-30529Shared CWE-352
CVE-2025-49077Shared CWE-352
CVE-2023-45011Shared CWE-352
CVE-2023-1937Shared CWE-352
CVE-2024-27197Shared CWE-352

Affected Assets

mozilla
firefox
≤ 150.0
mozilla
thunderbird
≤ 150.0

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)
  • V3.3.2
  • V3.5.1
  • V10.2.1

Mitigating Controls (NIST 800-53 r5) AI

SA-11 Developer Testing and Evaluation good match

Developer testing and evaluation can discover missing input validation through analysis or test cases.

SC-5 Denial-of-service Protection good match

SC-5 directly limits the effects of resource-exhaustion events that constitute uncontrolled consumption.

SC-6 Resource Availability good match

SC-6 enforces explicit allocation limits on resources, structurally preventing the weakness from occurring.

SI-10 Information Input Validation good match

SI-10 directly requires validity checks on information inputs, structurally preventing improper or missing validation.

AC-3 Access Enforcement partial match

Access enforcement requires verifying that state-changing requests originate from the authenticated user rather than a forged cross-site source.

SA-15 Development Process, Standards, and Tools partial match

Requiring documented development standards and tools can embed input-validation practices into the engineering process.

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.PS-06 partial match
blocks

Secure SDLC practices directly require anti-CSRF controls such as tokens or SameSite attributes.

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.5.24 Information security incident management planning and preparation partial match
finds

Pre-agreed severity-based prioritization and resource allocation during incident triage reduce the likelihood that an attacker-induced resource exhaustion will overwhelm the organization before corrective action is taken.

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-20, a class-level weakness, and none of its children carries one either.
  • No fine-grained STIG row for CWE-400, a class-level weakness. Rules are authored against its narrower children: CWE-770.

References