Memory leak in nanopb
Description
Nanopb is a small code-size Protocol Buffers implementation. In Nanopb before versions 0.4.4 and 0.3.9.7, decoding specifically formed message can leak memory if dynamic allocation is enabled and an oneof field contains a static submessage that contains a dynamic field, and the message being decoded contains the submessage multiple times. This is rare in normal messages, but it is a concern when untrusted data is parsed. This is fixed in versions 0.3.9.7 and 0.4.4. The following workarounds are available: 1) 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. 2) Set the type of the submessage field inside oneof to FT_POINTER. This way the whole submessage will be dynamically allocated and the problematic code is not executed. 3) Use an arena allocator for nanopb, to make sure all memory can be released afterwards.
Affected packages
Versions sourced from the GitHub Security Advisory.
| Package | Affected versions | Patched versions |
|---|---|---|
nanopbPyPI | >= 0.3.2, < 0.3.9.7 | 0.3.9.7 |
nanopbPyPI | >= 0.4.0, < 0.4.4 | 0.4.4 |
Affected products
1Patches
14fe23595732bFix memory leak with oneofs and PB_ENABLE_MALLOC (#615)
1 file changed · +6 −3
pb_decode.c+6 −3 modified@@ -464,14 +464,17 @@ static bool checkreturn decode_static_field(pb_istream_t *stream, pb_wire_type_t } case PB_HTYPE_ONEOF: - *(pb_size_t*)iter->pSize = iter->pos->tag; - if (PB_LTYPE(type) == PB_LTYPE_SUBMESSAGE) + if (PB_LTYPE(type) == PB_LTYPE_SUBMESSAGE && + *(pb_size_t*)iter->pSize != iter->pos->tag) { /* We memset to zero so that any callbacks are set to NULL. - * Then set any default values. */ + * This is because the callbacks might otherwise have values + * from some other union field. */ memset(iter->pData, 0, iter->pos->data_size); pb_message_set_to_defaults((const pb_field_t*)iter->pos->ptr, iter->pData); } + *(pb_size_t*)iter->pSize = iter->pos->tag; + return func(stream, iter->pos, iter->pData); default:
Vulnerability mechanics
Generated on May 9, 2026. Inputs: CWE entries + fix-commit diffs from this CVE's patches. Citations validated against bundle.
References
6- github.com/advisories/GHSA-85rr-4rh9-hhwhghsaADVISORY
- nvd.nist.gov/vuln/detail/CVE-2020-26243ghsaADVISORY
- github.com/nanopb/nanopb/blob/2b48a361786dfb1f63d229840217a93aae064667/CHANGELOG.txtghsax_refsource_MISCWEB
- github.com/nanopb/nanopb/commit/4fe23595732b6f1254cfc11a9b8d6da900b55b0cghsax_refsource_MISCWEB
- github.com/nanopb/nanopb/issues/615ghsax_refsource_MISCWEB
- github.com/nanopb/nanopb/security/advisories/GHSA-85rr-4rh9-hhwhghsax_refsource_CONFIRMWEB
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