{"id":"CVE-2025-4565","aliases":["GHSA-8qvm-5x2c-j2w7","PYSEC-2026-1806"],"url":"https://o3.security/vulnerability/CVE-2025-4565","summary":"Unbounded recursion in Python Protobuf","details":"### Summary\nAny project that uses Protobuf pure-Python backend to parse untrusted Protocol Buffers data containing an arbitrary number of **recursive groups**, **recursive messages** or **a series of [`SGROUP`](https://protobuf.dev/programming-guides/encoding/#groups) tags** can be corrupted by exceeding the Python recursion limit.\n\nReporter: Alexis Challande, Trail of Bits Ecosystem Security Team\n[ecosystem@trailofbits.com](mailto:ecosystem@trailofbits.com)\n\nAffected versions: This issue only affects the [pure-Python implementation](https://github.com/protocolbuffers/protobuf/tree/main/python#implementation-backends) of protobuf-python backend. This is the implementation when `PROTOCOL_BUFFERS_PYTHON_IMPLEMENTATION=python` environment variable is set or the default when protobuf is used from Bazel or pure-Python PyPi wheels. CPython PyPi wheels do not use pure-Python by default.\n\nThis is a Python variant of a [previous issue affecting protobuf-java](https://github.com/protocolbuffers/protobuf/security/advisories/GHSA-735f-pc8j-v9w8).\n\n### Severity\nThis is a potential Denial of Service. Parsing nested protobuf data creates unbounded recursions that can be abused by an attacker.\n\n### Proof of Concept\nFor reproduction details, please refer to the unit tests [decoder_test.py](https://github.com/protocolbuffers/protobuf/blob/main/python/google/protobuf/internal/decoder_test.py#L87-L98) and [message_test](https://github.com/protocolbuffers/protobuf/blob/main/python/google/protobuf/internal/message_test.py#L1436-L1478)\n\n### Remediation and Mitigation\nA mitigation is available now. Please update to the latest available versions of the following packages:\n* protobuf-python(4.25.8, 5.29.5, 6.31.1)","published":"2025-06-16T14:50:40.906Z","modified":"2026-08-12T15:13:30.778220Z","cvss":null,"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"PyPI","name":"protobuf","fixedVersion":"4.25.8"},{"ecosystem":"PyPI","name":"protobuf","fixedVersion":"5.29.5"},{"ecosystem":"PyPI","name":"protobuf","fixedVersion":"6.31.1"}],"fix":{"url":"https://github.com/protocolbuffers/protobuf/commit/17838beda2943d08b8a9d4df5b68f5f04f26d901","label":"protocolbuffers/protobuf@17838be"},"references":[{"type":"WEB","url":"https://github.com/protocolbuffers/protobuf/"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/4xxx/CVE-2025-4565.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2025-4565"},{"type":"FIX","url":"https://github.com/protocolbuffers/protobuf/commit/17838beda2943d08b8a9d4df5b68f5f04f26d901"},{"type":"PACKAGE","url":"https://pypi.org/project/protobuf/"},{"type":"WEB","url":"https://github.com/protocolbuffers/protobuf/security/advisories/GHSA-735f-pc8j-v9w8"},{"type":"WEB","url":"https://github.com/protocolbuffers/protobuf/security/advisories/GHSA-8qvm-5x2c-j2w7"},{"type":"PACKAGE","url":"https://github.com/protocolbuffers/protobuf"},{"type":"WEB","url":"https://github.com/protocolbuffers/protobuf/blob/main/python/google/protobuf/internal/decoder_test.py#L87-L98"},{"type":"WEB","url":"https://github.com/protocolbuffers/protobuf/blob/main/python/google/protobuf/internal/message_test.py#L1436-L1478"},{"type":"WEB","url":"https://github.com/protocolbuffers/protobuf/tree/main/python#implementation-backends"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T15:13:30.778220Z"}}