CVE-2021-23177

Privilege escalation via symlink target ACL modification

Published Aug 23, 2022 · Updated Aug 3, 2024

Improper link resolution in libarchive before 3.5.2 allows local users to gain privileges when a victim extracts a crafted archive. archive_write_disk_set_acls passes a symlink pathname to acl_set_file without checking the entry type, so Linux follows the link and writes the archived ACL to its target. Exploitation requires a victim to extract an attacker-supplied archive with ACL restoration enabled; the target ACL change can grant elevated file access.

CVSS severity7.3
High
EPSS probability0.39%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper link resolution in libarchive before 3.5.2 allows local users to gain privileges when a victim extracts a crafted archive. archive_write_disk_set_acls passes a symlink pathname to acl_set_file without checking the entry type, so Linux follows the link and writes the archived ACL to its target. Exploitation requires a victim to extract an attacker-supplied archive with ACL restoration enabled; the target ACL change can grant elevated file access.

The record

CVE
CVE-2021-23177
Published
Aug 23, 2022
Updated
Aug 3, 2024
Vendor
libarchive
Product
libarchive
Classifications
CWE-59, T1204.002, T1222.002
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 23, 2022CVE 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=Fixed in libarchive 3.5.2

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

libarchive · libarchiveversion=Fixed in libarchive 3.5.2

Published CVSS scores

7.3Red HatCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:L
7.8NVDCVSS:3.1/AV:L/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.

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)
Vectorlocal
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-59Improper Link Resolution Before File Access ('Link Following')
T1204.002Malicious File
T1222.002Linux and Mac File and Directory Permissions Modification

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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