http4k: HmacSha256.hash (despite the Hmac naming) computed a plain unkeyed digest; clarified by deprecation in favour of Sha256.hash / Sha256.hmac

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

8.2 · CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N · score source

EPSS

No dated EPSS signal available.

As published by the source; long descriptions are shortened.

Impact The HmacSha256 class contained two functions: - hash(payload) — a plain unkeyed SHA-256 digest. The Hmac prefix in the class name was misleading; this function has no key parameter, so it could never have been an HMAC. - hmacSHA256(key, data) — a properly keyed HMAC-SHA256. A reader who didn't engage with the function signature could in principle have assumed HmacSha256.hash(payload) was somehow keyed, but the absence of any key parameter made that misuse unlikely in practice. Who is affected: any downstream caller who read the class name and used HmacSha256.hash as a message authentication code without noticing it takes no key. Verified at v6.47.2.0: zero internal misuse in http4k itself. Both production usages of HmacSha256.hash (AWS SigV4 canonical-request hashing in AwsSignatureV4Signer.kt and x-amz-content-sha256 in awsExtensions.kt) are AWS-spec-correct uses of plain SHA-256; every keyed hmacSHA256(key, data) call passes a real key. The advisory exists so any downstream…

Published by the source

19 Jun 2026, 21:16 UTC

Last modified by the source

19 Jun 2026, 21:16 UTC

Source last checked

26 Oct 2026, 16:53 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-m4w9-hjfw-vwj4

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# Patch Next advisory brief: GHSA-m4w9-hjfw-vwj4

Advisory: http4k: `HmacSha256.hash` (despite the `Hmac` naming) computed a plain unkeyed digest; clarified by deprecation in favour of `Sha256.hash` / `Sha256.hmac`
IDs: GHSA-m4w9-hjfw-vwj4
Record: https://patchnext.com/advisories/ghsa-m4w9-hjfw-vwj4 (revision 1, source checked 26 Oct 2026, 16:53 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.2)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: org.http4k:http4k-core 6.49.0.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- Maven org.http4k:http4k-core: affected < 6.49.0.0; fixed in 6.49.0.0

## Suggested inspection (read-only)
- Maven org.http4k:http4k-core: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on org.http4k:http4k-core.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-m4w9-hjfw-vwj4 (GitHub-reviewed advisory GHSA-m4w9-hjfw-vwj4 lists affected ranges: Maven org.http4k:http4k-core >=0 <6.49.0.0)

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