CVE-2021-41991Network attack vector

Remote daemon crash via certificate-cache index overflow

Published Oct 18, 2021 · Updated Aug 4, 2024

Integer overflow in strongSwan 4.2.10 through 5.9.3 allows remote attackers to crash the IKE daemon via certificate-cache replacement. When the 32-slot in-memory cache is full, the index calculation can overflow for a large random value, producing a negative out-of-bounds index and double-dereference. The default-enabled charon.cert_cache must be filled with many distinct certificate encodings, usually requiring thousands of requests, and the expected result is a segmentation fault.

CVSS severity7.5
High
EPSS probability5.20%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Integer overflow in strongSwan 4.2.10 through 5.9.3 allows remote attackers to crash the IKE daemon via certificate-cache replacement. When the 32-slot in-memory cache is full, the index calculation can overflow for a large random value, producing a negative out-of-bounds index and double-dereference. The default-enabled charon.cert_cache must be filled with many distinct certificate encodings, usually requiring thousands of requests, and the expected result is a segmentation fault.

The record

CVE
CVE-2021-41991
Published
Oct 18, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-190, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 18, 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 vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
5.0NIST NVDAV:N/AC:L/Au:N/C:N/I:N/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-190Integer Overflow or Wraparound
T1499.004Application or System Exploitation

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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