CVE-2021-21401

HIGHNVD 7.17.1—
EchelonGraph scoreMEDIUM confidence

This high-severity CVE scores 7.1 under NVD CVSS v3. EPSS exploit probability: 1.8%, top 24% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, nvd
Trending — 3 sources updated this week
7.1
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS: 2%CVSS: 7.1Exploit: NoneExposed: 0

A fix is available — apply it.

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.

CVSS v3
7.1
EG Score
7.1(medium)
EG Risk
37(Track)
EG Risk 37/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity71% × 45%
Exploitation2% × 40%
Automatability30% × 15%
Action: Routine — remediate on your standard cadence.
EPSS
76.3%
KEV
Not listed

Published

March 23, 2021

Last Modified

November 21, 2024

References (8)

Patch Availability(1)

Vendor / EcosystemFixed in / PatchReleasedSource
ubuntunanopb (0.4.1-1ubuntu0.1~esm1) @ focal2026-05-26ubuntu

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

Affected Packages

(1 across 1 ecosystem)
PyPI(1)
PackageVulnerable rangeFixed inDependents
nanopb0.3.9.4.post3 ... 0.4.5.dev1234 (71 versions)0.4.5—

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

All Vendor Advisories

(1)

Every vendor that published an advisory referencing this CVE — pulled from our cve_vendor_advisories aggregation. Click any row for the vendor's original advisory page.

Data Freshness Timeline

(refreshed 11× in last 7d / 49× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

Showing the most recent 100 of 104 total refreshes for this CVE.

  1. 2026-07-23 01:57 UTCEG score recompute
  2. 2026-07-22 22:43 UTCEG score recompute
  3. 2026-07-22 14:05 UTCEPSS rescore
  4. 2026-07-21 15:22 UTCEPSS rescore
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  9. 2026-07-18 23:29 UTCOSV refresh
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  1. 2026-07-06 02:21 UTCEPSS rescore
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  7. 2026-07-02 16:57 UTCEPSS rescore
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  9. 2026-07-01 06:48 UTCOSV refresh
  10. 2026-06-30 23:20 UTCEPSS rescore
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  27. 2026-06-21 14:54 UTCEPSS rescore
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  29. 2026-06-21 01:58 UTCEPSS rescore
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  31. 2026-06-19 19:24 UTCEPSS rescore
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  40. 2026-06-13 11:13 UTCOSV refresh
  41. 2026-06-12 23:10 UTCEPSS rescore
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  43. 2026-06-11 13:58 UTCEPSS rescore
  44. 2026-06-10 22:16 UTCEPSS rescore
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  72. 2026-05-26 19:30 UTCEG score recompute
  73. 2026-05-26 19:30 UTCVendor advisory
  74. 2026-05-26 13:42 UTCEPSS rescore
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Frequently asked(5)

What is CVE-2021-21401?
CVE-2021-21401 is a high vulnerability published on March 23, 2021. 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…
When was CVE-2021-21401 disclosed?
CVE-2021-21401 was first published in the National Vulnerability Database on March 23, 2021, with the most recent update on November 21, 2024. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-21401 actively exploited?
CVE-2021-21401 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 76.3% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2021-21401?
CVE-2021-21401 has a CVSS v3 base score of 7.1 (NVD).
How do I remediate CVE-2021-21401?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-21401, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

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