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Vulnerability record · CVE-2021-41991 · published 18 October 2021

CVE-2021-41991: Strongswan integer overflow vulnerability

Strongswan · Strongswan

The in-memory certificate cache in strongSwan before 5.9.4 has a remote integer overflow upon receiving many requests with different certificates to fill the cache and later trigger the replacement of cache entries. The code attempts to select a less-often-used cache entry by means of a random number generator, but this is not done correctly. Remote code execution might be a slight possibility.

7.5 CVSS 3.1 High EPSS 5.3% · top 7.7% CWE-190 · Integer overflow
7.5CVSS 3.1 base score, v2 5.0
5.3%EPSS exploitation probability, 30 days
NoNot in CISA KEV
25Affected product versions listed by NVD
16References
17 Jun 2026Last modified by NVD

Description

The in-memory certificate cache in strongSwan before 5.9.4 has a remote integer overflow upon receiving many requests with different certificates to fill the cache and later trigger the replacement of cache entries. The code attempts to select a less-often-used cache entry by means of a random number generator, but this is not done correctly. Remote code execution might be a slight possibility.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected products

25 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://cert-portal.siemens.com/productcert/pdf/ssa-539476.pdf PatchThird Party Advisory
https://github.com/strongswan/strongswan/releases/tag/5.9.4 Third Party Advisory
https://lists.debian.org/debian-lts-announce/2021/10/msg00014.html Mailing ListThird Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/5FJSATD2R2XHTG4P63GCMQ2
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/WQSQ3BEC22NF4NCDZVCT4P3
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/Y3TQ32JLJOBJDB2EJKSX2PB
https://www.debian.org/security/2021/dsa-4989 Third Party Advisory
https://www.strongswan.org/blog/2021/10/18/strongswan-vulnerability-%28cve-2021-41991%29.html
https://cert-portal.siemens.com/productcert/pdf/ssa-539476.pdf PatchThird Party Advisory
https://github.com/strongswan/strongswan/releases/tag/5.9.4 Third Party Advisory
https://lists.debian.org/debian-lts-announce/2021/10/msg00014.html Mailing ListThird Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/5FJSATD2R2XHTG4P63GCMQ2
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/WQSQ3BEC22NF4NCDZVCT4P3
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/Y3TQ32JLJOBJDB2EJKSX2PB
https://www.debian.org/security/2021/dsa-4989 Third Party Advisory
https://www.strongswan.org/blog/2021/10/18/strongswan-vulnerability-%28cve-2021-41991%29.html

Track CVE-2021-41991 inside VULONE

Watch it alongside the ransomware crews, C2 infrastructure and forum chatter that reference it, query it through the API and pull it into your SIEM over TAXII.

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Source: NIST National Vulnerability Database (record CVE-2021-41991), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.