CVE-2026-1525
Nodejs Undici ≤ 6.24.0
Raw vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:LSummary
CVE-2026-1525 is a medium-severity HTTP Request/Response Smuggling (CWE-444) vulnerability in Nodejs Undici. Its CVSS base score is 6.5 (Medium).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 40th 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 SC-7 (Boundary Protection) 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-2026-1525 affects the Undici HTTP client library for Node.js, allowing the creation of malformed HTTP/1.1 requests with duplicate Content-Length headers. This occurs when headers are passed as flat arrays containing case-variant names, such as "Content-Length" and "content-length", which Undici does not normalize or deduplicate. Applications are impacted if they use low-level APIs like undici.request() or undici.Client with such header arrays, or if they accept user-controlled header names without case-normalization.
Remote attackers with network access can exploit this vulnerability without authentication or user interaction, as indicated by its CVSS v3.1 base score of 6.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L). By supplying crafted header arrays, attackers can trigger denial of service on strict HTTP parsers in proxies or servers, which reject requests with conflicting Content-Length values via 400 Bad Request responses. In multi-tier deployments where front-end intermediaries and backends interpret duplicates differently—such as one selecting the first value and another the last—this enables HTTP request smuggling (CWE-444), potentially leading to access control bypass, cache poisoning, or credential hijacking.
Mitigation guidance and patches are detailed in official advisories, including the Undici GitHub security advisory (GHSA-2mjp-6q6p-2qxm) and OpenJSF security advisories. Additional technical context appears in the related HackerOne report (3556037) and RFC 9110 section on Content-Length handling.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-11685
Vulnerability Data
Undici allows duplicate HTTP Content-Length headers when they are provided in an array with case-variant names (e.g., Content-Length and content-length). This produces malformed HTTP/1.1 requests with multiple conflicting Content-Length values on the wire. Who is impacted: * Applications using undici.request(),…
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undici.Client, or similar low-level APIs with headers passed as flat arrays * Applications that accept user-controlled header names without case-normalization Potential consequences: * Denial of Service: Strict HTTP parsers (proxies, servers) will reject requests with duplicate Content-Length headers (400 Bad Request) * HTTP Request Smuggling: In deployments where an intermediary and backend interpret duplicate headers inconsistently (e.g., one uses the first value, the other uses the last), this can enable request smuggling attacks leading to ACL bypass, cache poisoning, or credential hijacking
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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V4.1.3V4.2.4V1.5.3V4.1.1
Mitigating Controls (NIST 800-53 r5) AI
Boundary protection at external interfaces can enforce consistent HTTP request/response parsing rules between intermediaries and endpoints.
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.
Configuration management can enforce uniform HTTP parsing rules across intermediaries, directly mitigating inconsistent interpretation.
Network monitoring can detect smuggling attempts via anomalous HTTP traffic or logs, while eliminating the inconsistency directly aids detection of such events.
Network protections can enforce consistent HTTP proxy/firewall behavior to block smuggling, and removing the weakness helps prevent unauthorized access via request smuggling.
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 HTTP request smuggling vulnerabilities in intermediary components.
Network security controls can enforce consistent HTTP parsing and proxy behavior that mitigates request smuggling.
Secure network services include hardening proxies and gateways against inconsistent HTTP interpretation.
Secure SDLC practices require threat modeling and testing for HTTP parsing inconsistencies in intermediaries.
Application security requirements can mandate strict HTTP message validation and canonicalization.
Secure architecture principles include consistent protocol handling and defense-in-depth for proxies.