CVE-2026-86140

Local code execution via unchecked parenthesis appends

Published Sep 5, 2026 · Updated Sep 8, 2026

Stack-based buffer overflow in libxml2 before 2.15.4 allows local users to execute code by triggering DTD validation. xmlSnprintfElements in valid.c appends opening and closing parentheses to a caller-supplied stack buffer with strcat without first checking the remaining capacity. Reaching this validation path with crafted XML can overwrite stack memory, enabling code execution or a process crash.

CVSS severity8.0
High
EPSS probability0.15%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Stack-based buffer overflow in libxml2 before 2.15.4 allows local users to execute code by triggering DTD validation. xmlSnprintfElements in valid.c appends opening and closing parentheses to a caller-supplied stack buffer with strcat without first checking the remaining capacity. Reaching this validation path with crafted XML can overwrite stack memory, enabling code execution or a process crash.

The record

CVE
CVE-2026-86140
Published
Sep 5, 2026
Updated
Sep 8, 2026
Vendor
XMLSoft
Product
libxml2
Classifications
CWE-121, T1203
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 5, 2026CVE publishedPublication date reported by the CVE source.
  2. Sep 8, 2026Record 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 <2.15.4

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

XMLSoft · libxml2version=0 <2.15.4

Published CVSS scores

8.0MITRECVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/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)
Vectorlocal
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-121Stack-based Buffer Overflow
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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