Invalid free() call in Nanopb
Description
Nanopb is a small code-size Protocol Buffers implementation in ansi C. In Nanopb before versions 0.3.9.8 and 0.4.5, decoding 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. This has been fixed in versions 0.3.9.8 and 0.4.5. See referenced GitHub Security Advisory for more information including workarounds.
Affected packages
Versions sourced from the GitHub Security Advisory.
| Package | Affected versions | Patched versions |
|---|---|---|
nanopbPyPI | >= 0.3.2, < 0.3.9.8 | 0.3.9.8 |
nanopbPyPI | >= 0.4.0, < 0.4.5 | 0.4.5 |
Affected products
1Patches
2e2f0ccf939d9Fix invalid free() with oneof (#647)
1 file changed · +8 −0
pb_decode.c+8 −0 modified@@ -1203,6 +1203,14 @@ static bool pb_release_union_field(pb_istream_t *stream, pb_field_iter_t *field) pb_release_single_field(&old_field); + if (PB_ATYPE(field->type) == PB_ATYPE_POINTER) + { + /* Initialize the pointer to NULL to make sure it is valid + * even in case of error return. */ + *(void**)field->pField = NULL; + field->pData = NULL; + } + return true; }
4a375a560651Fix invalid free() with oneof (#647)
1 file changed · +8 −1
pb_decode.c+8 −1 modified@@ -1150,7 +1150,14 @@ static bool pb_release_union_field(pb_istream_t *stream, pb_field_iter_t *iter) * This shouldn't fail unless the pb_field_t structure is corrupted. */ if (!pb_field_iter_find(iter, new_tag)) PB_RETURN_ERROR(stream, "iterator error"); - + + if (PB_ATYPE(iter->pos->type) == PB_ATYPE_POINTER) + { + /* Initialize the pointer to NULL to make sure it is valid + * even in case of error return. */ + *(void**)iter->pData = NULL; + } + return true; }
Vulnerability mechanics
Generated on May 9, 2026. Inputs: CWE entries + fix-commit diffs from this CVE's patches. Citations validated against bundle.
References
8- github.com/advisories/GHSA-7mv5-5mxh-qg88ghsaADVISORY
- nvd.nist.gov/vuln/detail/CVE-2021-21401ghsaADVISORY
- github.com/nanopb/nanopb/blob/c9124132a604047d0ef97a09c0e99cd9bed2c818/CHANGELOG.txtghsax_refsource_MISCWEB
- github.com/nanopb/nanopb/commit/4a375a560651a86726e5283be85a9231fd0efe9cghsaWEB
- github.com/nanopb/nanopb/commit/e2f0ccf939d9f82931d085acb6df8e9a182a4261ghsax_refsource_MISCWEB
- github.com/nanopb/nanopb/issues/647ghsax_refsource_MISCWEB
- github.com/nanopb/nanopb/security/advisories/GHSA-7mv5-5mxh-qg88ghsax_refsource_CONFIRMWEB
- github.com/pypa/advisory-database/tree/main/vulns/nanopb/PYSEC-2021-432.yamlghsaWEB
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