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How CVE-2026-54147 Works
An issue exists in DigestAuthProvider.verify: the configured algorithm parameter is silently ignored—every verification uses MD5 regardless of configuration. Deployments believing they are running SHA-256 Digest authentication are silently inheriting MD5’s collision weaknesses, including documented attack paths against Digest schemes that rely on the hash being collision-resistant. The bug has been present since `DigestAuthProvider` was introduced (commit 8a52b615b1, 2021). Any application using `http4k-security-digest` for HTTP Digest authentication is affected.
When an application configures `DigestAlgorithm.SHA-256` (or any algorithm other than MD5), the `verify` method ignores that configuration and hardcodes MD5 for all nonce and response hash computations. This means the security posture is silently downgraded without any warning or error. Attackers who can capture a Digest authentication handshake can leverage MD5’s known collision attacks (e.g., chosen-prefix collisions) to forge valid responses or impersonate users, depending on the broader application context.
The fix, released in http4k CE v6.50.0.0 and http4k EE LTS v5.42.0.0 / v4.51.0.0, hashes with the configured algorithm instead of hardcoded MD5.
DailyCVE Form
Platform: http4k-security-digest
Version: ≤6.49.0.0 / ≤5.41.0.0 / ≤4.50.0.0
Vulnerability: Algorithm ignored → MD5
Severity: Moderate (CVSS 6.5)
Date: 2026-06-16
Prediction: Patch already released 2026-05-31
What Undercode Say
Analytics of the vulnerability surface:
- Affected module: `org.http4k:http4k-security-digest`
– Affected versions: - Community (v6.x): 6.49.0.0 and below → fixed in 6.50.0.0
- Enterprise LTS (v5.x): 5.41.0.0 and below → fixed in 5.42.0.0
- Enterprise LTS (v4.x): 4.50.0.0 and below → fixed in 4.51.0.0
- Introduced: commit `8a52b615b1` (2021)
- Discovered: 2026-05-30 during Claude-assisted security review
- CVE assigned: 2026-06-12 by GitHub
- Public disclosure: 2026-06-16
- Advisory: GHSA-vxxm-wwqh-mh47
Check your dependency:
Maven mvn dependency:tree | grep http4k-security-digest Gradle ./gradlew dependencies | grep http4k-security-digest Direct inspection (pom.xml) grep -A5 "http4k-security-digest" pom.xml
Verify the fix is applied (Kotlin example):
// Before (vulnerable) — algorithm parameter ignored DigestAuthProvider( credentials = myCredentials, algorithm = DigestAlgorithm.SHA-256 // silently ignored, MD5 used ) // After (fixed) — algorithm parameter respected DigestAuthProvider( credentials = myCredentials, algorithm = DigestAlgorithm.SHA-256 // now actually uses SHA-256 )
Exploit (Educational Purposes!)
⚠️ WARNING: The following is for educational and defensive purposes only. Do not use against systems without explicit authorization.
A captured Digest authentication response can be exploited because the algorithm is forced to MD5:
1. Capture a Digest challenge-response (network sniffing or log access):
– Client sends `Authorization: Digest username=”user”, realm=”…”, nonce=”…”, uri=”…”, response=”“`
– The `response` value is computed as: `MD5(MD5(username:realm:password):nonce:MD5(method:uri))`
2. Because MD5 is used regardless of configuration, an attacker can:
– Perform offline MD5 collision attacks against the captured hash
– Use chosen-prefix collision techniques (e.g., using tools likehashclash) to craft an alternate credential that produces the same MD5 digest
– Replay the forged response against the same realm
3. The attacker does not need to know the actual password—only to produce a collision with the captured MD5 hash.Conceptual attack flow (not a working exploit) Capture a valid Digest response with MD5 hash echo "MD5(username:realm:password):nonce:MD5(method:uri)" > target_hash.txt Use MD5 collision tools (e.g., hashclash, fastcoll) to find collision This is computationally intensive but feasible for MD5 fastcoll -p prefix.bin -o col1.bin col2.bin Replay forged Authorization header with collision payload curl -H "Authorization: Digest username=attacker, response=<collision_hash>" https://target/api
Protection
1. Upgrade immediately to the fixed versions:
- v6.x (Community): upgrade to 6.50.0.0 or higher
- v5.x (Enterprise LTS): upgrade to 5.42.0.0 or higher
- v4.x (Enterprise LTS): upgrade to 4.51.0.0 or higher
- For http4k EE subscribers, fixed LTS versions are available through the dedicated http4k Maven instance:
Contact: [email protected]
3. If unable to upgrade immediately:
- Do not rely on the configured `algorithm` parameter
- Assume MD5 is in use regardless of configuration
- Treat Digest credentials as low-trust
- Consider additional authentication layers (e.g., mutual TLS, API keys)
- Shorten nonce validity windows to reduce replay window
- Monitor for unusual authentication patterns
4. Verify the fix:
// After upgrade, confirm the algorithm is respected val provider = DigestAuthProvider(credentials, DigestAlgorithm.SHA-256) // provider now uses SHA-256, not MD5
Impact
- Confidentiality: MD5’s collision weaknesses allow attackers to potentially forge Digest authentication responses
- Integrity: A captured Digest response can be leveraged to impersonate legitimate users
- Availability: Not directly impacted; however, successful impersonation can lead to unauthorized data modification or deletion
- Scope: Any application using `http4k-security-digest` for HTTP Digest authentication
- Attack complexity: Requires capturing a valid Digest authentication handshake (network observation, log access, etc.)—non-trivial but feasible in many deployments
- Remediation effort: Low—upgrade to the patched version; no code changes required beyond version bump
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Sources:
Reported By: github.com
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