A fault in the Bouncy Castle cryptographic libraries causes a BadTagException when GCM decryption is performed in certain chunked patterns. The vulnerability is classified as CWE‑1068, an error handling bypass. When the library receives a ciphertext broken into chunks at particular boundaries, the authentication tag verification fails and the decryption operation aborts, which may terminate or hang the caller. Because the error results from a failure to validate the authentication tag, no data is disclosed or altered and the effect is limited to the application’s availability.

The issue affects the Legion of the Bouncy Castle Inc. BC‑LTS component in versions 2.73.0 through 2.73.10 and the BC‑FJA component in versions 2.1.0 through 2.1.2. These versions run on Linux x86_64 with AVX or AVX‑512f instruction sets and involve the modules gcm128w, gcm512w, gcm128w.C, and gcm512w.C.

The CVSS score of 5.1 indicates moderate severity, and the EPSS score of < 1% suggests a low probability of exploitation. The vulnerability is not listed in the CISA KEV catalog. Based on the description, it is inferred that an attacker who can supply untrusted ciphertext to a decryption API that uses BC‑LTS may trigger the BadTagException by chunking the data at the problematic boundaries, causing a denial‑of‑service condition. No remote code execution or data disclosure is possible.