Http4s: CookieJar middleware matches by substring, leaking cookies cross-origin

published 2026-09-15 54 d ago modified 2026-09-16 53 d ago also GHSA-grh8-3p95-f9rr , EUVD-2026-79191

cvss: 6.8; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.5%; EPSS 0.5% chance of exploitation in 30 days, percentile 43%
public exploits: 0; none known

Http4s is a Scala interface for HTTP services. Prior to 0.23.35 and 1.0.0-M47, The CookieJar client middleware uses unanchored substring checks instead of RFC 6265 domain and path matching when deciding whether to attach a stored cookie. A cookie for example.com can consequently be sent to an attacker-controlled hostname such as evilexample.com when an application using the same jar makes an attacker-influenced outbound request. This exposes session or authentication cookies and can enable hijacking of the application’s outbound sessions. This issue is fixed in versions 0.23.35 and 1.0.0-M47.

Patch / fix

fixed in 3 links 3

maven org.http4s:http4s-client_2.12 0.23.35
maven org.http4s:http4s-client_2.13 0.23.35, 1.0.0-M47
maven org.http4s:http4s-client_3 0.23.35, 1.0.0-M47

github.com/http4s/http4s@c0a37f3 commit
github.com/http4s/http4s/releases/tag/v0.23.35 release
github.com/http4s/http4s/releases/tag/v1.0.0-M47 release

CISA SSVC

Exploitation: none
Automatable: no
Technical impact: partial
Assessed: 53 d ago (2026-09-16)

Exploit prediction

0.51% chance of exploitation in the next 30 days, higher than 43% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	3.1	6.8	CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:N/A:N
GitHub	3.1	6.8	CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:N/A:N

Affected packages

ecosystem	package	affected	fixed in
maven	org.http4s:http4s-client_2.12	<0.23.35	0.23.35
maven	org.http4s:http4s-client_2.13	<0.23.35 >=1.0.0-M1, <1.0.0-M47	0.23.35 1.0.0-M47
maven	org.http4s:http4s-client_3	<0.23.35 >=1.0.0-M1, <1.0.0-M47	0.23.35 1.0.0-M47

Affected products

http4s http4s

Classification

Weakness

CWE-565 Reliance on Cookies without Validation and Integrity Checking
CWE-1275 Sensitive Cookie with Improper SameSite Attribute

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary