CVE-2021-3518Network attack vector

Memory corruption via dangling XInclude entity pointers

Published May 18, 2021 · Updated Aug 3, 2024

Use-after-free in XInclude processing in XMLSoft libxml2 before 2.9.11 allows attackers to corrupt memory via crafted XML. xmlXIncludeDoProcess descends into entity-reference nodes whose pointers can be left dangling when DTD data is removed, then scans or modifies freed structures. Exploitation requires XInclude processing after DTD removal, including xmllint with --xinclude and --dropdtd; the stale access can crash the process or corrupt its memory.

CVSS severity8.6
High
EPSS probability3.65%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Use-after-free in XInclude processing in XMLSoft libxml2 before 2.9.11 allows attackers to corrupt memory via crafted XML. xmlXIncludeDoProcess descends into entity-reference nodes whose pointers can be left dangling when DTD data is removed, then scans or modifies freed structures. Exploitation requires XInclude processing after DTD removal, including xmllint with --xinclude and --dropdtd; the stale access can crash the process or corrupt its memory.

The record

CVE
CVE-2021-3518
Published
May 18, 2021
Updated
Aug 3, 2024
Vendor
XMLSoft
Product
libxml2
Classifications
CWE-416, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 18, 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=libxml2 2.9.11

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

XMLSoft · libxml2version=libxml2 2.9.11

Published CVSS scores

8.6Red HatCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H
8.8NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/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.

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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
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-416Use After Free
T1203Exploitation for Client Execution

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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