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Vulnerabilities

Vulnerability · CVE-2026-40561

Starlet versions through 0.31 for Perl allows HTTP Request Smuggling via Improper Header Precedence.

Published May 3, 2026 · catalog updated Jun 17, 2026 · Starlet versions through 0.31

Check if you run it

No confirmed exploitation is on record for CVE-2026-40561. EPSS is 0.43%. Act only if a listed version of Starlet versions through 0.31 is installed.

Gaps on this record

  • The stored product name is a package slug. The name on this page is taken from the title (Starlet versions through 0.31).
  • 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
Medium5.3
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.43%
Remediation
Advisory link
Affected products
cpe kazuho/starlet

Starlet versions through 0.31 for Perl allows HTTP Request Smuggling via Improper Header Precedence. Starlet incorrectly prioritizes "Content-Length" over "Transfer-Encoding: chunked" when both headers are present in an HTTP request. Per RFC 7230 3.3.3, Transfer-Encoding must take precedence. An attacker could exploit this to smuggle malicious HTTP requests via a front-end reverse proxy.

Are you affected?

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

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • cpe kazuho/starletversion unspecified

How to fix CVE-2026-40561

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-2026-40561. EPSS is 0.43%. Act only if a listed version of Starlet versions through 0.31 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 0.43%. 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. May 3, 2026 · NIST NVD

    Detected

    Starlet versions through 0.31 for Perl allows HTTP Request Smuggling via Improper Header Precedence. Starlet incorrectly prioritizes "Content-Length" over "Transfer-Encoding: chunked" when both headers are present in an HTTP request. Per RFC 7230 3.3.3, Transfer-Encoding must take precedence. An attacker could exploit this to smuggle malicious HTTP requests via a front-end reverse proxy.

  2. Jun 17, 2026 · NIST NVD

    Updated

    Starlet versions through 0.31 for Perl allows HTTP Request Smuggling via Improper Header Precedence. Starlet incorrectly prioritizes "Content-Length" over "Transfer-Encoding: chunked" when both headers are present in an HTTP request. Per RFC 7230 3.3.3, Transfer-Encoding must take precedence. An attacker could exploit this to smuggle malicious HTTP requests via a front-end reverse proxy.

Sources

  • CVE.orgVulnerability recordCVE-2026-40561

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-40561

    30-day exploitation probability 0.4%

    first.org
  • NIST NVDVulnerability recordCVE-2026-40561

    Starlet versions through 0.31 for Perl allows HTTP Request Smuggling via Improper Header Precedence. Starlet incorrectly prioritizes "Content-Length" over "Transfer-Encoding: chunked" when both headers are present in an HTTP request. Per RFC 7230 3.3.3, Transfer-Encoding must ta

    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.