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CVE-2026-40561

25
FAUCET Score

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.

First published: May 3, 2026Last modified: May 7, 2026

Impacted Technologies

VendorProductVersion(s)CPE
>= 0, <= 0.31CPE match
cpe:2.3:a:kazuho:starlet:*:*:*:*:*:perl:*:*
<= 0.31CPE matchmatch criteria
cpe:2.3:a:kazuho:starlet:*:*:*:*:*:perl:*:*

CVSS Data

CVSS version used by this source: 3.1

5.3MEDIUM

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
NONE
Integrity Impact
LOW
Availability Impact
NONE
Exploitability Score
3.9
Impact Score
1.4
CvssVersion
3.1

Exploit Intelligence

EPSS Score
0.36%
Probability of exploitation in next 30 days
EPSS Percentile
29.0%
Percentile rank of EPSS score among Peer Group
As of 2026-07-28
Model: v2026.06.15
This CVE's current EPSS score of 0.0036 is in the 18th percentile among its peer group of 23,725 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.1 Bluesky, 0.0 Mastodon, and 0.4 GitHub mentions.

Media Mentions

The average CVE in this peer group has 0.0 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (1)

github_advisorypatch availablevia nvd_reference
View patch

References

datatracker.ietf.org / doc/html/rfc7230
Third Party Advisory
github.com / kazuho/Starlet/commit/a7d5dfd1862aafa43e5eaca0fdb6acf4cc15b2d0.patch
Patch
metacpan.org / release/KAZUHO/Starlet-0.32/changes
openwall.com / lists/oss-security/2026/05/03/1
Mailing ListThird Party Advisory