Http4s: DigestAuth allows replay of captured requests
The DigestAuth replay defence stores lastNc + 1 rather than the nonce-count (nc) value it just accepted. When a legitimate client sends non-contiguous nc values (parallel or retried requests, as browsers do), the server's counter lags behind the highest nc seen, and a captured Authorization header can be replayed multiple times.
Impact
A passive observer can turn one captured Digest-authenticated request into several replayed authenticated (state-changing) requests, defeating the core replay protection Digest provides over Basic.
Preconditions
- Application uses
DigestAuth. - Attacker can passively observe at least one legitimate digest request.
- Legitimate client emits an
ncmore than one greater than the last, for instance from a parallel or retried request.
Workarounds
- Deploy over TLS so requests cannot be captured.
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Java / Kotlin (Maven) | org.http4s:http4s-ember-core_2.12 | < 0.23.35 | 0.23.35 |
| Java / Kotlin (Maven) | org.http4s:http4s-ember-core_2.13 | < 0.23.35, >= 1.0.0-M1, < 1.0.0-M47 | 0.23.35, 1.0.0-M47 |
| Java / Kotlin (Maven) | org.http4s:http4s-ember-core_3 | < 0.23.35, >= 1.0.0-M1, < 1.0.0-M47 | 0.23.35, 1.0.0-M47 |
References
- CVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N- Weakness (CWE)
CWE-294- Platform
- Java / Kotlin (Maven)
- Package
org.http4s:http4s-ember-core_2.12, org.http4s:http4s-ember-core_2.13, org.http4s:http4s-ember-core_3- Disclosed
- 15.09.2026
- Updated
- 11.10.2026 13:20
Sources and licenses
OSV / GitHub Advisory Database - GHSA-9xww-74xv-gjfp - CC BY 4.0
Vulnerability history: org.http4s:http4s-ember-core_2.13
All published vulnerabilities of this package (Java / Kotlin (Maven)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 11
- First → latest
- 09.2025 09.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- Critical 1
- High 7
- Medium 3
Disclosures per year
- 2025: 1
- 2026: 10
-
Http4s: DigestAuth allows replay of captured requests this entry
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