Raw vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:HCVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.
Summary
CVE-2026-4700 is a critical-severity Authentication Bypass Using an Alternate Path or Channel (CWE-288) vulnerability in Mozilla Firefox. Its CVSS base score is 9.8 (Critical).
Operationally, exploitation aligns with the MITRE ATT&CK technique Data Obfuscation (T1001); ranked at the 38th 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-25 (Reference Monitor) and AC-3 (Access 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-2026-4700 is a mitigation bypass vulnerability in the Networking: HTTP component of Mozilla Firefox and Thunderbird. It affects versions of Firefox prior to 149, Firefox ESR prior to 140.9, Thunderbird prior to 149, and Thunderbird prior to 140.9. The issue is classified under CWE-288 (Authentication Bypass Using an Alternate Path or Channel) with a CVSS v3.1 base score of 9.8, indicating critical severity due to its network accessibility, low complexity, lack of required privileges or user interaction, and high impacts on confidentiality, integrity, and availability.
Any unauthenticated remote attacker can exploit this vulnerability over the network with low complexity and no user interaction. Successful exploitation allows the attacker to bypass security mitigations in the HTTP networking stack, potentially leading to arbitrary code execution, data theft, or system compromise on affected browsers or email clients.
Mozilla security advisories (MFSA 2026-20, 22, 23, 24) and the associated Bugzilla entry (2003766) confirm the vulnerability was addressed in the specified fixed releases. Mitigation requires updating to Firefox 149, Firefox ESR 140.9, Thunderbird 149, or Thunderbird 140.9, with no additional workarounds mentioned.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-14817
Vulnerability Data
Mitigation bypass in the Networking: HTTP component. This vulnerability was fixed in Firefox 149, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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- 7 hardening rules · 3 OS baselines
V4.1.3V4.2.4V6.4.3V6.6.1
Mitigating Controls (NIST 800-53 r5) AI
Requires a tamperproof, always-invoked reference monitor that structurally blocks bypass via any alternate path.
Enforces authorization checks on every logical access path, eliminating unauthenticated alternate channels.
Mandates unique identification and authentication for all organizational users, covering the primary authentication requirement.
Controls all external and key internal interfaces, reducing the chance of unauthenticated alternate channels.
Validating HTTP inputs at the intermediary prevents malformed messages from being interpreted inconsistently downstream.
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.
Network monitoring can detect smuggling attempts via anomalous HTTP traffic or logs, while eliminating the inconsistency directly aids detection of such events.
Requiring authentication on every channel and path directly eliminates alternate-path bypasses.
Enforcing authorizations and least privilege across all access vectors prevents unauthenticated alternate paths.
Protecting networks and environments from unauthorized logical access blocks bypass via undocumented channels.
Configuration management can enforce uniform HTTP parsing rules across intermediaries, directly mitigating inconsistent interpretation.
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.5.15 only requires defining a topic-specific access control policy and determining requirements; it does not itself enforce, implement or configure any access rules that would stop an alternate unauthenticated path from being exploitable.
Access rights provisioning and review prevent bypass via unmonitored or alternate channels.
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` (higher-evidence rows only; rows rated `none` are excluded).
Oracle Linux 8 (2 rules)
- V-248598 There must be no ".shosts" files on the OL 8 operating system. blocks CWE-288
- V-248827 OL 8 must not have the rsh-server package installed. blocks CWE-288
Oracle Linux 9 (2 rules)
- V-271757 OL 9 file systems must not contain shosts.equiv files. blocks CWE-288
- V-271758 OL 9 file systems must not contain .shosts files. blocks CWE-288
RHEL 7 (3 rules)
- V-204440 Red Hat Enterprise Linux operating systems version 7.2 or newer using Unified Extensible Firmware Interface (UEFI) must require authentication upon booting into single-user and maintenance modes. blocks CWE-288
- V-204442 The Red Hat Enterprise Linux operating system must not have the rsh-server package installed. blocks CWE-288
- V-204424 The Red Hat Enterprise Linux operating system must not allow accounts configured with blank or null passwords. blocks CWE-288