{"id":"CVE-2021-21401","aliases":["GHSA-7mv5-5mxh-qg88","PYSEC-2021-432"],"url":"https://o3.security/vulnerability/CVE-2021-21401","summary":"nanopb vulnerable to invalid free() call with oneofs and PB_ENABLE_MALLOC","details":"### Impact\nDecoding a specifically formed message can cause invalid `free()` or `realloc()` calls if the message type contains an `oneof` field, and the `oneof` directly contains both a pointer field and a non-pointer field. If the message data first contains the non-pointer field and then the pointer field, the data of the non-pointer field is incorrectly treated as if it was a pointer value. Such message data rarely occurs in normal messages, but it is a concern when untrusted data is parsed.\n\n### Patches\nPreliminary patch is available on git for [0.4.x](https://github.com/nanopb/nanopb/commit/e2f0ccf939d9f82931d085acb6df8e9a182a4261) and [0.3.x](https://github.com/nanopb/nanopb/commit/4a375a560651a86726e5283be85a9231fd0efe9c) branches. The fix will be released in versions 0.3.9.8 and 0.4.5 once testing has been completed.\n\n### Workarounds\nFollowing workarounds are available:\n* Set the option `no_unions` for the oneof field. This will generate fields as separate instead of C union, and avoids triggering the problematic code.\n* Set the type of all fields inside the oneof to `FT_POINTER`. This ensures that the data contained inside the `union` is always a valid pointer.\n* Heap implementations that guard against invalid `free()` provide a partial mitigation. Depending on the message type, the pointer value may be attacker controlled and can be used to bypass heap protections.\n\n### References\nBug report: https://github.com/nanopb/nanopb/issues/647\n\n### For more information\nIf you have any questions or comments about this advisory, comment on the bug report linked above.","published":"2021-03-23T18:15:13.160Z","modified":"2026-07-09T10:21:15.288826Z","cvss":{"score":7.1,"severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:L"},"epss":null,"cisaKev":null,"exploitsKnown":2,"affectedPackages":[{"ecosystem":"PyPI","name":"nanopb","fixedVersion":"0.3.9.8"},{"ecosystem":"PyPI","name":"nanopb","fixedVersion":"0.4.5"}],"fix":{"url":"https://github.com/nanopb/nanopb/commit/e2f0ccf939d9f82931d085acb6df8e9a182a4261","label":"nanopb/nanopb@e2f0ccf"},"references":[{"type":"ADVISORY","url":"https://github.com/nanopb/nanopb/blob/c9124132a604047d0ef97a09c0e99cd9bed2c818/CHANGELOG.txt#L1"},{"type":"REPORT","url":"https://github.com/nanopb/nanopb/issues/647"},{"type":"FIX","url":"https://github.com/nanopb/nanopb/commit/e2f0ccf939d9f82931d085acb6df8e9a182a4261"},{"type":"FIX","url":"https://github.com/nanopb/nanopb/security/advisories/GHSA-7mv5-5mxh-qg88"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2021-21401"},{"type":"WEB","url":"https://github.com/nanopb/nanopb/commit/4a375a560651a86726e5283be85a9231fd0efe9c"},{"type":"PACKAGE","url":"https://github.com/nanopb/nanopb"},{"type":"WEB","url":"https://github.com/pypa/advisory-database/tree/main/vulns/nanopb/PYSEC-2021-432.yaml"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-07-09T10:21:15.288826Z"}}