CVE-2021-44732Network attack vector

Heap corruption via failed session copy cleanup

Published Dec 20, 2021 · Updated Nov 3, 2025

Double free in Mbed TLS allows remote attackers to corrupt heap memory by triggering an out-of-memory session-copy failure. After ssl_session_copy leaves two structures pointing to the same ticket buffer, normal cleanup through mbedtls_ssl_session_free and mbedtls_ssl_free releases that buffer twice. Exploitation requires an allocation failure in mbedtls_ssl_set_session or mbedtls_ssl_get_session; the published consequence is heap corruption, not a demonstrated code-execution path.

CVSS severity9.8
Critical
EPSS probability2.58%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Double free in Mbed TLS allows remote attackers to corrupt heap memory by triggering an out-of-memory session-copy failure. After ssl_session_copy leaves two structures pointing to the same ticket buffer, normal cleanup through mbedtls_ssl_session_free and mbedtls_ssl_free releases that buffer twice. Exploitation requires an allocation failure in mbedtls_ssl_set_session or mbedtls_ssl_get_session; the published consequence is heap corruption, not a demonstrated code-execution path.

The record

CVE
CVE-2021-44732
Published
Dec 20, 2021
Updated
Nov 3, 2025
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-415
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 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

7.5NIST NVDAV:N/AC:L/Au:N/C:P/I:P/A:P
9.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/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)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-415Double Free

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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