Vulnerability in Http4s

CVE-2026-69206

Http4s is a Scala interface for HTTP services. Prior to 0.23.35 and 1.0.0-M47, DigestAuth replay protection records lastNc plus one instead of the highest nonce-count value it has accepted. When a legitimate client sends noncontiguous nc values because of parallel or retried requests, the stored counter remains below the accepted maximum, allowing a passive observer to replay a captured Authorization header multiple times. Successful replays execute authenticated requests, including state-changing operations, as the captured user. This issue is fixed in versions 0.23.35 and 1.0.0-M47.

Published · last modified .

CVSS v3 metric

CVSS v3 base score 5.9 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N.

EPSS exploit prediction

EPSS: 0.004 (33.7th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 34th percentile — 33.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-69206: held from 0.004 to 0.004.

EPSS over last 30 days · oldest: 0.004 · newest: 0.004 · change: 0.000

Affected products

  • Http4s — versions < 0.23.35, >= 1.0.0-M1, < 1.0.0-M47

Weakness classification (CWE)

References

Frequently asked questions

What is CVE-2026-69206?
CVE-2026-69206 is a medium-severity vulnerability in Http4s, classified under Authentication Bypass by Capture-replay. CVSS score: 5.9/10. Published 2026-09-15.
How severe is CVE-2026-69206?
Medium severity. CVSS v3 base score is 5.9 out of 10.