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Public proof of conceptFix available

CVE-2021-21401

A public proof of concept exists; no exploitation attested.

  • Published2021-03-23
  • Fixed in0.4.5 · 0.3.9.8
  • WeaknessCWE-763

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

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.

Timeline

dates in UTC
  1. 2021-03-2318:15CVE publishedNVD

Versions per branch

NVD · OSV
Nanopb project nanopb
BranchAffectedFixed in
0.4≥ 0.4.0, < 0.4.50.4.5
0.3< 0.3.9.80.3.9.8
0.3≥ 0.3.2, < 0.3.9.80.3.9.8

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

  • nanopbUbuntu:Pro:20.04:LTSall versions · fixed in 0.4.1-1ubuntu0.1~esm1
  • nanopbopenSUSE:Tumbleweedall versions · fixed in 0.4.5-1.3
  • nanopbDebian:14all versions · fixed in 0.4.4-2
  • nanopbDebian:13all versions · fixed in 0.4.4-2
  • nanopbDebian:12all versions · fixed in 0.4.4-2

Full record on NVD

Fix

  1. Update Nanopb project nanopb to 0.4.5 · 0.3.9.8

Advisories and patches

Detection

read 2026-11-01 01:02 UTC
Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof of concept
Metasploit modules
none listed
Metasploit Framework

Sources

  • CNACVSS 3.17.1known since 2026-10-23
  • NVDCVSS 3.17.1read 2026-10-23
  • NVDCVSS 2.05.5read 2026-10-23
  • CNAweakness (CWE)CWE-763known since 2026-10-23
  • FIRST EPSSEPSS score1.8 %2026-11-09
  • PoC-in-GitHubproof of concept1known since 2026-11-01
  • OSVaffected packages—
  • GitHub AdvisoriesadvisoryHIGH2024-08-30

Identifiers

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:L
Published
2021-03-23
Last Modified
2026-06-17
NVD status
Modified
GitHub Advisory
GHSA-7mv5-5mxh-qg88

Frequently asked questions

What is CVE-2021-21401?

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.

Is CVE-2021-21401 actively exploited?

Active exploitation of CVE-2021-21401 has not been confirmed. Its EPSS score was 1.8% on 2026-11-09, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-21401?

CVE-2021-21401 has a CVSS v3 base score of 7.1 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:L.

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