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Vulnerabilities

Vulnerability · CVE-2026-1525

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).

Published Mar 12, 2026 · catalog updated Jun 17, 2026 · Red Hat

Check if you run it

No confirmed exploitation is on record for CVE-2026-1525. EPSS is 0.51%. Act only if a listed version of Red Hat is installed.

Gaps on this record

  • No version range is stored. A customer cannot check an installed version against this record.
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
Critical9.8
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.51%
Remediation
Advisory link
Affected products
cpe nodejs/undici

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

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

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  • cpe nodejs/undiciversion unspecified

How to fix CVE-2026-1525

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-1525. EPSS is 0.51%. Act only if a listed version of Red Hat is installed.

Which versions are affected?

Affected version ranges are not on this record. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-444: HTTP Request Smuggling. EPSS 0.51%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Mar 12, 2026 · NIST NVD

    Detected

    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 * Applicati

  2. Jun 17, 2026 · NIST NVD

    Updated

    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 * Applicati

Sources

  • CSAF AdvisoriesVendor advisoryRHSA-2026:9742:CVE-2026-1525

    A flaw was found in undici, a Node.js HTTP/1.1 client. A remote attacker could exploit this vulnerability by sending HTTP/1.1 requests that include duplicate Content-Length headers with different casing (e.g., "Content-Length" and "content-length"). This can lead to HTTP Request

    security.access.redhat.com
  • CVE.orgVulnerability recordCVE-2026-1525

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-1525

    30-day exploitation probability 0.5%

    first.org
  • NIST NVDVulnerability recordCVE-2026-1525

    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: *

    nvd.nist.gov

References

Freshness

Last verified in this catalog Oct 18, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.