CVE-2021-33574Network attack vector

Application crash via shallow thread-attribute copy

Published May 25, 2021 · Updated Aug 3, 2024

Use-after-free in GNU C Library 2.32 and 2.33 allows attackers to crash an application through a crafted mq_notify call. In mq_notify's SIGEV_THREAD path, a shallow memcpy of pthread_attr_t retains a pointer to a separately allocated non-default CPU-affinity mask after the caller frees the original attributes. The affected application must invoke mq_notify with SIGEV_THREAD and a non-default affinity mask; the documented consequence is an application crash.

CVSS severity9.8
Critical
EPSS probability2.87%
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 GNU C Library 2.32 and 2.33 allows attackers to crash an application through a crafted mq_notify call. In mq_notify's SIGEV_THREAD path, a shallow memcpy of pthread_attr_t retains a pointer to a separately allocated non-default CPU-affinity mask after the caller frees the original attributes. The affected application must invoke mq_notify with SIGEV_THREAD and a non-default affinity mask; the documented consequence is an application crash.

The record

CVE
CVE-2021-33574
Published
May 25, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-416, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 25, 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?

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

9.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
7.5NIST NVDAV:N/AC:L/Au:N/C:P/I:P/A:P

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
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

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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