nanopb vulnerable to invalid free() call with oneofs and PB_ENABLE_MALLOC
Impact
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.
Patches
Preliminary patch is available on git for 0.4.x and 0.3.x branches. The fix will be released in versions 0.3.9.8 and 0.4.5 once testing has been completed.
Workarounds
Following workarounds are available:
- Set the option
no_unionsfor the oneof field. This will generate fields as separate instead of C union, and avoids triggering the problematic code. - Set the type of all fields inside the oneof to
FT_POINTER. This ensures that the data contained inside theunionis always a valid pointer. - 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.
References
Bug report: https://github.com/nanopb/nanopb/issues/647
For more information
If you have any questions or comments about this advisory, comment on the bug report linked above.
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | nanopb | >= 0.3.2, < 0.3.9.8, >= 0.4.0, < 0.4.5 | 0.3.9.8, 0.4.5 |
References
- https://github.com/nanopb/nanopb/security/advisories/GHSA-7mv5-5mxh-qg88
- https://github.com/nanopb/nanopb/commit/e2f0ccf939d9f82931d085acb6df8e9a182a4261
- https://github.com/nanopb/nanopb/issues/647
- https://github.com/nanopb/nanopb/blob/c9124132a604047d0ef97a09c0e99cd9bed2c818/CHANGELOG.txt#L1
- https://nvd.nist.gov/vuln/detail/CVE-2021-21401
- https://github.com/nanopb/nanopb/commit/4a375a560651a86726e5283be85a9231fd0efe9c
- https://github.com/nanopb/nanopb
- https://github.com/pypa/advisory-database/tree/main/vulns/nanopb/PYSEC-2021-432.yaml
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:L- Weakness (CWE)
CWE-763- Platform
- Python (PyPI)
- Package
nanopb- Disclosed
- 23.03.2021
- Updated
- 11.10.2026 13:19
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2021-432 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-7mv5-5mxh-qg88 - CC BY 4.0
Vulnerability history: nanopb
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 2
- First → latest
- 11.2020 03.2021
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 1
- Medium 1
Disclosures per year
- 2020: 1
- 2021: 1
- 2022: 0
- 2023: 0
- 2024: 0
- 2025: 0
- 2026: 0
-
nanopb vulnerable to invalid free() call with oneofs and PB_ENABLE_MALLOC this entry
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