Summary The DER parser used for application-supplied private keys did not safely validate encoded length values before converting them to "Int" values or allocating arrays. A malformed private-key file could encode a length that overflowed or wrapped around, or request an allocation much larger than the available input. This could cause parsing errors or an uncaught "OutOfMemoryError", potentially terminating the application process. Details The issue was in "DerReader.readLength()" and primitive readers such as "readInteger()". "readLength()" previously accepted up to 127 length octets and accumulated them into an "Int": length = (length shl 8) or nextByte This permitted integer overflow. For example: - "0x1_0000_0001" wrapped to "1". - "0x8000_0000" wrapped to "Int.MIN_VALUE". Primitive readers then allocated memory based on the resulting value without first checking it against the remaining input: val bytes = ByteArray(length) data.get(bytes) A six-byte DER value declaring a 1 GiB INTEGER caused an immediate "OutOfMemoryError" when tested with a constrained JVM heap. Because "OutOfMemoryError" is not an "Exception", it is not caught by the public-key authentication error handling and may terminate the application process. A zero-length DER INTEGER is also invalid, but it does not produce "BigInteger.ZERO": Java throws "NumberFormatException" when constructing a "BigInteger" from an empty byte array. No weakened or usable cryptographic key has been demonstrated through this issue. Attack Requirements The affected DER parser processes private-key material explicitly supplied by the application through APIs such as: - "SshClient.authenticatePublicKey()" - "SshKeys.decodePemPrivateKey()" - "SshSigning.sign()" - "SshSigning.getPublicKey()" The DER input is not populated from SSH server host keys or agent-forwarding requests. Exploitation therefore requires a user or application to load an attacker-provided private-key file. The issue is not remotely exploitable by an SSH server. Impact Successful exploitation can cause: - Incorrect DER length interpretation due to integer wraparound - Excessive memory allocation - An uncaught "OutOfMemoryError" - Loss of availability of the affected application process There is no demonstrated confidentiality or integrity impact. Remediation The DER parser now: - Rejects indefinite lengths - Explicitly limits long-form lengths to "Int.SIZE_BYTES" (four octets) and rejects values above "Int.MAX_VALUE" - Accumulates long-form lengths in a "Long" before converting to "Int" - Rejects truncated and non-minimal length encodings - Checks declared lengths against the remaining input before allocation or advancing the input position - Rejects zero-length DER INTEGER, BIT STRING, and OBJECT IDENTIFIER values where an empty encoding is invalid - Rejects non-canonical DER INTEGER encodings with redundant sign octets The bounds checks are implemented in shared DER reader helpers and apply to INTEGER, OCTET STRING, BIT STRING, OBJECT IDENTIFIER, SEQUENCE, context-specific values, and skipped values. PKCS#1 RSA and SEC1 EC private keys pass application-supplied DER directly through these helpers. PKCS#8 input is parsed by the JCA provider, and OpenSSH private keys use a separate wire-format parser rather than "DerReader".