CVE-2021-21401Public exploitNetwork attack vector

Memory corruption via uncleared oneof pointer

Published Mar 23, 2021 · Updated Aug 3, 2024

Memory corruption in Nanopb 0.3.2 through 0.3.9.7 and 0.4.0 through 0.4.4 allows attackers to crash applications via crafted messages. In pb_release_union_field, the decoder switches from a non-pointer oneof member to a pointer member without clearing the union storage, then passes attacker-controlled data to free() or realloc(). The path requires PB_ENABLE_MALLOC and a oneof containing pointer and non-pointer fields; the consequence ranges from an application crash to heap corruption.

CVSS severity7.1
High
EPSS probability1.81%
Next 30 days · Sep 17, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Memory corruption in Nanopb 0.3.2 through 0.3.9.7 and 0.4.0 through 0.4.4 allows attackers to crash applications via crafted messages. In pb_release_union_field, the decoder switches from a non-pointer oneof member to a pointer member without clearing the union storage, then passes attacker-controlled data to free() or realloc(). The path requires PB_ENABLE_MALLOC and a oneof containing pointer and non-pointer fields; the consequence ranges from an application crash to heap corruption.

The record

CVE
CVE-2021-21401
Published
Mar 23, 2021
Updated
Aug 3, 2024
Vendor
Petteri Aimonen
Product
Nanopb
Classifications
CWE-763, T1499
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Mar 23, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=>= 0.3.2, <= 0.3.9.7
  2. Affected versionversion=>= 0.4.0, <= 0.4.4

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Petteri Aimonen · Nanopbversion=>= 0.3.2, <= 0.3.9.7; version=>= 0.4.0, <= 0.4.4

Published CVSS scores

5.5NIST NVDAV:N/AC:L/Au:S/C:N/I:P/A:P
7.1GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:L

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-763Release of Invalid Pointer or Reference
T1499Endpoint Denial of Service

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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