GHSA-m4w9-hjfw-vwj4: HmacSha256.hash computed a plain unkeyed digest

Description#

The HmacSha256 class contained two functions:

• hash(payload) - a plain unkeyed SHA-256 digest. It takes no key parameter, so it was never an HMAC despite the class name.
• hmacSHA256(key, data) - a properly keyed HMAC-SHA256.

A downstream caller who read the class name and used HmacSha256.hash as a message authentication code without noticing it takes no key would get no authentication. There is no internal misuse in http4k itself: both production usages of HmacSha256.hash (AWS SigV4 canonical-request hashing and x-amz-content-sha256) are spec-correct uses of plain SHA-256, and every keyed call passes a real key.

The fix introduces Sha256.hash(input) (unkeyed digest) and Sha256.hmac(key, input) (keyed HMAC-SHA256). HmacSha256 is deprecated; existing callers continue to work via deprecation shims.

Affected http4k modules & versions#

• http4k-core
  • 6.48.x and below

Mitigation#

Upgrade to the fixed version and migrate to Sha256.hash or Sha256.hmac according to intent.

If you cannot upgrade and need a real HMAC-SHA256, use javax.crypto.Mac.getInstance("HmacSHA256") with a SecretKeySpec, or the existing hmacSHA256(key, data), which was always correctly implemented.

Resolution timeline#

References

• GitHub advisory: https://github.com/http4k/http4k/security/advisories/GHSA-m4w9-hjfw-vwj4