Summary
Memory leak in Nanopb
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 the submessage field inside oneof to
FT_POINTER. This way the whole submessage will be dynamically allocated and the problematic code is not executed. - Use an arena allocator for nanopb, to make sure all memory can be released afterwards.
References
Bug report: https://github.com/nanopb/nanopb/issues/615
For more information
If you have any questions or comments about this advisory, comment on the bug report linked above.
Impact
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.
The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths. Typical impact: varies by context: data corruption, logic bypass, or denial of service.
CVE-2020-26243 has a CVSS score of 7.5 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.3.9.7, 0.4.4); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Preliminary patch is available on git and problem will be patched in versions 0.3.9.7 and 0.4.4 once testing has been completed.
Frequently Asked Questions
- What is CVE-2020-26243? CVE-2020-26243 is a medium-severity improper input validation vulnerability in nanopb (pip), affecting versions >= 0.3.2, <= 0.3.9.6. It is fixed in 0.3.9.7, 0.4.4. The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths.
- How severe is CVE-2020-26243? CVE-2020-26243 has a CVSS score of 7.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of nanopb are affected by CVE-2020-26243? nanopb (pip) versions >= 0.3.2, <= 0.3.9.6 is affected.
- Is there a fix for CVE-2020-26243? Yes. CVE-2020-26243 is fixed in 0.3.9.7, 0.4.4. Upgrade to this version or later.
- Is CVE-2020-26243 exploitable, and should I be worried? Whether CVE-2020-26243 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2020-26243 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2020-26243?
- Upgrade
nanopbto 0.3.9.7 or later - Upgrade
nanopbto 0.4.4 or later
- Upgrade