CVE-2021-39534Public exploit

Service crash via out-of-bounds comment parsing

Published Sep 20, 2021 · Updated Aug 4, 2024

Heap-buffer over-read in libslax 0.22.1 and earlier allows context-dependent attackers to crash a consuming process with crafted SLAX input. While testing whether input begins a comment, slaxIsCommentStart reads one byte past the heap buffer when crafted input ends at the boundary. A consuming application must parse the attacker-controlled content; the demonstrated consequence is an AddressSanitizer-detected abort, not code execution.

CVSS severity8.8
High
EPSS probability1.27%
Next 30 days · Sep 17, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Heap-buffer over-read in libslax 0.22.1 and earlier allows context-dependent attackers to crash a consuming process with crafted SLAX input. While testing whether input begins a comment, slaxIsCommentStart reads one byte past the heap buffer when crafted input ends at the boundary. A consuming application must parse the attacker-controlled content; the demonstrated consequence is an AddressSanitizer-detected abort, not code execution.

The record

CVE
CVE-2021-39534
Published
Sep 20, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-787, T1499.004
Attack vector
Unavailable
Privileges
Unavailable

Timeline

How it unfolded

  1. Sep 20, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 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 vectorUnavailable in this record.
Required privilegesUnavailable in this record.

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

6.8NIST NVDAV:N/AC:M/Au:N/C:P/I:P/A:P
8.8NIST NVDCVSS: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)
VectorUnavailable
PrivilegesUnavailable
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-787Out-of-bounds Write
T1499.004Application or System Exploitation

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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