CVE-2026-107283: 
Java vulnerability analysis and mitigation

CVE-2026-107283 is a cryptographic weakness in the AsyncHttpClient (AHC) Java library where HTTP Digest authentication client nonces (cnonce) are generated using ThreadLocalRandom — a non-cryptographic pseudorandom number generator — instead of a cryptographically secure source. This affects AHC versions >= 2.0.0 and < 2.16.1 (2.x branch) and >= 3.0.0 and < 3.0.12 (3.x branch). The vulnerability was disclosed on August 9, 2026, and patched in versions 2.16.1 and 3.0.12. It carries a CVSS v3.1 base score of 3.7 (Low) (GitHub Advisory).

The root cause is classified as CWE-338 (Use of Cryptographically Weak Pseudo-Random Number Generator). Specifically, Realm.Builder.newCnonce() in Realm.java seeded the 8-byte client nonce from ThreadLocalRandom.current().nextBytes(), whose output is predictable from observed values. RFC 7616 section 3.3 requires the cnonce to be unpredictable, as it protects the Digest exchange against chosen-plaintext and credential precomputation attacks. Notably, other authentication schemes in the same codebase (NTLM, SCRAM) already used SecureRandom for their nonces — Digest was the sole exception. The fix replaces ThreadLocalRandom with a ThreadLocal<SecureRandom> instance in Realm.Builder, matching the security posture of the other schemes (GitHub Advisory, Patch Commit 2.x, Patch Commit 3.x).

Successful exploitation reduces the unpredictability of the HTTP Digest authentication exchange, potentially allowing a network attacker who can observe or infer the ThreadLocalRandom generator state to perform chosen-plaintext attacks or precompute valid credential responses. The primary impact is a low-severity confidentiality risk — an attacker could potentially recover or bypass authentication credentials used by Java applications built on vulnerable AHC versions. Integrity and availability are not directly affected (GitHub Advisory).

There is no public proof-of-concept exploit and no evidence of in-the-wild exploitation at this time (GitHub Advisory). The EPSS score is approximately 0.263%, reflecting a low probability of exploitation in the near term. The vulnerability is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog. Exploitation requires high attack complexity — the attacker must be able to observe sufficient ThreadLocalRandom output to infer generator state, making opportunistic exploitation unlikely. No threat actor attribution has been reported.

Upgrade AsyncHttpClient to version 3.0.12 (3.x branch) or 2.16.1 (2.x branch), which replace ThreadLocalRandom with SecureRandom for cnonce generation. No application-level workaround is available for vulnerable versions. Organizations should also review applications that used AHC with HTTP Digest authentication during the vulnerable window and consider rotating any potentially exposed credentials (GitHub Advisory, AHC 2.16.1 Release, AHC 3.0.12 Release).