CVE-2021-45960Public exploit

Process crash via prefixed-attribute allocation overflow

Published Jan 1, 2022 · Updated May 5, 2025

Integer overflow in Expat before 2.4.3 allows attackers to crash XML-parsing processes with a tag containing many prefixed attributes. The storeAtts function derives m_nsAttsPower from the prefix count, left-shifts a signed value by at least 29 bits, and passes the resulting nsAttsSize to realloc without rejecting overflow. Reaching the flaw requires a multi-gigabyte XML document; affected operations can allocate too little memory, free memory, or encounter undefined behavior, depending on the architecture and shift count.

CVSS severity8.8
High
EPSS probability4.23%
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 Expat before 2.4.3 allows attackers to crash XML-parsing processes with a tag containing many prefixed attributes. The storeAtts function derives m_nsAttsPower from the prefix count, left-shifts a signed value by at least 29 bits, and passes the resulting nsAttsSize to realloc without rejecting overflow. Reaching the flaw requires a multi-gigabyte XML document; affected operations can allocate too little memory, free memory, or encounter undefined behavior, depending on the architecture and shift count.

The record

CVE
CVE-2021-45960
Published
Jan 1, 2022
Updated
May 5, 2025
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-190, T1499
Attack vector
Unavailable
Privileges
Unavailable

Timeline

How it unfolded

  1. Jan 1, 2022CVE publishedPublication date reported by the CVE source.
  2. May 5, 2025Record 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 vectorUnavailable in this record.
Required privilegesUnavailable in this record.

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

8.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
8.8CISA-ADPCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

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)
VectorUnavailable
PrivilegesUnavailable
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-190Integer Overflow or Wraparound
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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