CVE-2021-36976Public exploitNetwork attack vector

Application crash via desynchronized RAR5 window state

Published Jul 20, 2021 · Updated Nov 3, 2025

Use-after-free in the RAR5 reader in libarchive 3.4.1 through 3.5.1 allows remote attackers to crash an application via a crafted archive. The reader lets archive-declared window parameters desynchronize window_mask from the allocated window_buf size, so copy_string reads freed or invalid heap memory. A user or embedding application must process the malicious RAR5 file; published scoring identifies no confidentiality or integrity impact.

CVSS severity6.5
Medium
EPSS probability2.84%
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 the RAR5 reader in libarchive 3.4.1 through 3.5.1 allows remote attackers to crash an application via a crafted archive. The reader lets archive-declared window parameters desynchronize window_mask from the allocated window_buf size, so copy_string reads freed or invalid heap memory. A user or embedding application must process the malicious RAR5 file; published scoring identifies no confidentiality or integrity impact.

The record

CVE
CVE-2021-36976
Published
Jul 20, 2021
Updated
Nov 3, 2025
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-416, T1204.002
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 20, 2021CVE publishedPublication date reported by the CVE source.
  2. Nov 3, 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 vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

6.5National Vulnerability DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/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 exploitPublished

Weakness, pattern, technique

CWE-416Use After Free
T1204.002User Execution: Malicious File

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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