CVE-2021-31871Network attack vector

cpio crash via wrapped link-size allocation

Published Apr 30, 2021 · Updated Aug 3, 2024

Integer overflow in klibc cpio before 2.0.9 allows attackers to crash the utility by processing a crafted archive on 64-bit systems. In copyin_link(), casting c_filesize to unsigned int before adding one wraps UINT_MAX to zero, producing a null pointer that is dereferenced. The flaw is limited to 64-bit builds and interrupts the cpio process; Ubuntu notes that its initramfs use does not parse untrusted data.

CVSS severity7.5
High
EPSS probability1.88%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Integer overflow in klibc cpio before 2.0.9 allows attackers to crash the utility by processing a crafted archive on 64-bit systems. In copyin_link(), casting c_filesize to unsigned int before adding one wraps UINT_MAX to zero, producing a null pointer that is dereferenced. The flaw is limited to 64-bit builds and interrupts the cpio process; Ubuntu notes that its initramfs use does not parse untrusted data.

The record

CVE
CVE-2021-31871
Published
Apr 30, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-190, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 30, 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?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
5.0NIST NVDAV:N/AC:L/Au:N/C:N/I:N/A:P

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-190Integer Overflow or Wraparound
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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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