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8.2
http4k: Misleading SHA-256 Digest in HmacSha256 Class
published 4 months ago
Summary
The HmacSha256 class in http4k had a function called hash that was supposed to be a secure message authentication code, but it was actually just a plain SHA-256 digest without a key. This could have led downstream callers to use it incorrectly. To fix this, update to http4k version 6.49.0.0 or later, which introduces new functions for secure hashing and migration paths for existing code.
What to do
- Update http4k org.http4k:http4k-core to version 6.49.0.0.
Affected software
| Ecosystem | Vendor | Product | Affected versions |
|---|---|---|---|
| maven | http4k | org.http4k:http4k-core |
< 6.49.0.0 Fix: upgrade to 6.49.0.0
|
Original advisory text
http4k: `HmacSha256.hash` (despite the `Hmac` naming) computed a plain unkeyed digest; clarified by deprecation in favour of `Sha256.hash` / `Sha256.hmac`
### 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 caller relying on the misleadingly-named API knows to migrate.
### Patches
Upgrade to **6.49.0.0** or later. The fix introduces:
- `Sha256.hash(input)` — unkeyed digest (the actual behaviour `HmacSha256.hash` provided).
- `Sha256.hmac(key, input)` — keyed HMAC-SHA256 (the behaviour the name implied).
`HmacSha256` is deprecated. Existing callers continue to work via deprecation shims; migrate to `Sha256.hash` or `Sha256.hmac` per intent.
### Workarounds
If you cannot upgrade and you need a real HMAC-SHA256, use `javax.crypto.Mac.getInstance("HmacSHA256")` with a `SecretKeySpec`. For an unkeyed SHA-256 digest, use `java.security.MessageDigest.getInstance("SHA-256")`. The keyed `hmacSHA256(key, data)` was always correctly implemented and is safe to use as-is.
### References
- Fix release: [v6.49.0.0](https://github.com/http4k/http4k/releases/tag/6.49.0.0)
- Background: [RFC 2104 — HMAC: Keyed-Hashing for Message Authentication](https://datatracker.ietf.org/doc/html/rfc2104)
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 caller relying on the misleadingly-named API knows to migrate.
### Patches
Upgrade to **6.49.0.0** or later. The fix introduces:
- `Sha256.hash(input)` — unkeyed digest (the actual behaviour `HmacSha256.hash` provided).
- `Sha256.hmac(key, input)` — keyed HMAC-SHA256 (the behaviour the name implied).
`HmacSha256` is deprecated. Existing callers continue to work via deprecation shims; migrate to `Sha256.hash` or `Sha256.hmac` per intent.
### Workarounds
If you cannot upgrade and you need a real HMAC-SHA256, use `javax.crypto.Mac.getInstance("HmacSHA256")` with a `SecretKeySpec`. For an unkeyed SHA-256 digest, use `java.security.MessageDigest.getInstance("SHA-256")`. The keyed `hmacSHA256(key, data)` was always correctly implemented and is safe to use as-is.
### References
- Fix release: [v6.49.0.0](https://github.com/http4k/http4k/releases/tag/6.49.0.0)
- Background: [RFC 2104 — HMAC: Keyed-Hashing for Message Authentication](https://datatracker.ietf.org/doc/html/rfc2104)
Internet-facing
60 days
Internal
At next upgrade
- Not known to be exploited
- Needs hands-on effort to exploit (estimated)
- Gives an attacker partial control (estimated)
Type
CWE-345Insufficient Verification of Data Authenticity
Timeline
Published19 Jun 2026
Updated19 Jun 2026
First seen19 Jun 2026
Sources
GHSA-m4w9-hjfw-vwj4 · GHSA
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