Http4s: FollowRedirect middleware leaks credentials over https->http same-authority redirect

published 2026-09-15 54 d ago modified 2026-09-16 53 d ago also EUVD-2026-79186

cvss: 5.9; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.3%; EPSS 0.3% chance of exploitation in 30 days, percentile 20%
public exploits: 0; none known

Http4s is a Scala interface for HTTP services. Prior to 0.23.35 and 1.0.0-M47, The FollowRedirect client middleware strips Authorization and Cookie headers only when a redirect changes authority, but authority comparison excludes the URI scheme. A same-authority redirect from HTTPS to HTTP therefore preserves credentials and transmits them over a plaintext connection. An attacker who can induce the downgrade and observe the network can capture those sensitive headers from applications using FollowRedirect. This issue is fixed in versions 0.23.35 and 1.0.0-M47.

Patch / fix

links 3

github.com/http4s/http4s@6e82571 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: 54 d ago (2026-09-15)

Exploit prediction

0.28% chance of exploitation in the next 30 days, higher than 20% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	3.1	5.9	CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

Affected products

http4s http4s

Classification

Weakness

CWE-200 Exposure of Sensitive Information to an Unauthorized Actor
CWE-319 Cleartext Transmission of Sensitive Information

References

Sources

CVE List CVE-2026-69212
NVD CVE-2026-69212

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