CVE-2026-1525
undici is vulnerable to Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
Description
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(), 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
INFO
Published Date :
March 12, 2026, 8:16 p.m.
Last Modified :
March 19, 2026, 5:29 p.m.
Remotely Exploit :
Yes !
Source :
ce714d77-add3-4f53-aff5-83d477b104bb
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 3.1 | MEDIUM | ce714d77-add3-4f53-aff5-83d477b104bb | ||||
| CVSS 3.1 | MEDIUM | MITRE-CVE | ||||
| CVSS 3.1 | CRITICAL | [email protected] |
Solution
- Update the undici library to the latest version.
- Ensure header names are case-normalized before sending.
- Configure intermediaries to reject duplicate headers.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-1525.
| URL | Resource |
|---|---|
| https://cna.openjsf.org/security-advisories.html | Vendor Advisory |
| https://cwe.mitre.org/data/definitions/444.html | Technical Description |
| https://github.com/nodejs/undici/security/advisories/GHSA-2mjp-6q6p-2qxm | Mitigation Vendor Advisory |
| https://hackerone.com/reports/3556037 | Permissions Required |
| https://www.rfc-editor.org/rfc/rfc9110.html#section-8.6 | Technical Description |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-1525 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-1525
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-1525 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-1525 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
Initial Analysis by [email protected]
Mar. 19, 2026
Action Type Old Value New Value Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H Added CPE Configuration OR *cpe:2.3:a:nodejs:undici:*:*:*:*:*:node.js:*:* versions up to (excluding) 6.24.0 *cpe:2.3:a:nodejs:undici:*:*:*:*:*:node.js:*:* versions from (including) 7.0.0 up to (excluding) 7.24.0 Added Reference Type openjs: https://cna.openjsf.org/security-advisories.html Types: Vendor Advisory Added Reference Type openjs: https://cwe.mitre.org/data/definitions/444.html Types: Technical Description Added Reference Type openjs: https://github.com/nodejs/undici/security/advisories/GHSA-2mjp-6q6p-2qxm Types: Mitigation, Vendor Advisory Added Reference Type openjs: https://hackerone.com/reports/3556037 Types: Permissions Required Added Reference Type openjs: https://www.rfc-editor.org/rfc/rfc9110.html#section-8.6 Types: Technical Description -
New CVE Received by ce714d77-add3-4f53-aff5-83d477b104bb
Mar. 12, 2026
Action Type Old Value New Value Added Description 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(), 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 Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L Added CWE CWE-444 Added Reference https://cna.openjsf.org/security-advisories.html Added Reference https://cwe.mitre.org/data/definitions/444.html Added Reference https://github.com/nodejs/undici/security/advisories/GHSA-2mjp-6q6p-2qxm Added Reference https://hackerone.com/reports/3556037 Added Reference https://www.rfc-editor.org/rfc/rfc9110.html#section-8.6