CVE-2025-1936
Mozilla Firefox ≤ 128.8.0
Raw vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:LSummary
CVE-2025-1936 is a high-severity Improper Neutralization of Null Byte or NUL Character (CWE-158) vulnerability in Mozilla Firefox. Its CVSS base score is 7.3 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 36th 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 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-2025-1936 is a vulnerability in the handling of jar: URLs within Mozilla Firefox and Thunderbird. These URLs retrieve local file content packaged in a ZIP archive, but the parser ignored the null byte and everything after it when extracting the content, while using a fake extension placed after the null byte to determine the content type. This flaw, classified under CWE-158 (Null Byte Interaction Error), enabled attackers to hide malicious code within a web extension by disguising it as another file type, such as an image. Versions of Firefox prior to 136, Firefox ESR prior to 128.8, Thunderbird prior to 136, and Thunderbird prior to 128.8 are affected.
The vulnerability carries a CVSS v3.1 base score of 7.3 (AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L), indicating it can be exploited remotely over the network by unauthenticated attackers with low complexity and no user interaction required. Exploitation allows limited impacts on confidentiality, integrity, and availability, primarily through the bypass of content type checks to deliver disguised malicious payloads, such as executable web extensions masquerading as benign files.
Mozilla has fixed this issue in Firefox 136, Firefox ESR 128.8, Thunderbird 136, and Thunderbird 128.8. Security advisories MFSA 2025-14, MFSA 2025-16, MFSA 2025-17, and MFSA 2025-18, along with Bugzilla entry 1940027, provide further details on the patch and recommend immediate updates to mitigate the risk.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2025-7441
Vulnerability Data
jar: URLs retrieve local file content packaged in a ZIP archive. The null and everything after it was ignored when retrieving the content from the archive, but the fake extension after the null was used to determine the type of…
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content. This could have been used to hide code in a web extension disguised as something else like an image. This vulnerability was fixed in Firefox 136, Firefox ESR 128.8, Thunderbird 136, and Thunderbird 128.8.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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V1.2.10
Mitigating Controls (NIST 800-53 r5) AI
Input validation directly requires neutralizing or rejecting malformed characters such as NUL before they reach downstream components.
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.
Secure SDLC practices directly require input neutralization and validation to prevent null-byte flaws.
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.
Security testing can detect null-byte flaws but does not itself implement the neutralization.
Secure development lifecycle mandates input validation and sanitization that directly prevents null-byte injection.
Application security requirements include explicit rules for neutralizing dangerous characters such as NUL.
Secure architecture principles reduce the likelihood of unsafe data flows but do not prescribe character neutralization.
Secure coding standards explicitly require proper neutralization of null bytes and other metacharacters.