Predictive Vulnerability Intelligence.

Product

  • Product
  • Pricing
  • Documentation

Company

  • About
  • Partnerships
  • Blog
  • Support

Legal

  • Terms
  • Privacy
  • Data Licensing

© 2026 FAUCET Technologies LLC. All rights reserved.

CVE-2021-41991

27
FAUCET Score

CVE-2021-41991 is an integer overflow vulnerability in the in-memory certificate cache of strongSwan versions prior to 5.9.4, also affecting Debian, Fedora, and Siemens products. This high-severity vulnerability (CVSS 7.5) can be exploited remotely with low complexity, leading to a denial of service, with a slight possibility of remote code execution. Despite its potential impact, there is no evidence of active exploitation, no public exploit code available (Metasploit, Nuclei, ExploitDB), and minimal community discussion or media coverage.

Impacted Technologies

VendorProductVersion(s)CPE
>= 4.2.10, < 5.9.4CPE matchmatch criteria
cpe:2.3:a:strongswan:strongswan:*:*:*:*:*:*:*:*
9.0CPE matchmatch criteria
cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:*
10.0CPE matchmatch criteria
cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:*
11.0CPE matchmatch criteria
cpe:2.3:o:debian:debian_linux:11.0:*:*:*:*:*:*:*
33CPE matchmatch criteria
cpe:2.3:o:fedoraproject:fedora:33:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

7.5HIGH

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

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
NONE
Integrity Impact
NONE
Availability Impact
HIGH
Exploitability Score
3.9
Impact Score
3.6
CvssVersion
3.1

Exploit Intelligence

EPSS Score
4.84%
Probability of exploitation in next 30 days
EPSS Percentile
91.1%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0484 is in the 84th percentile among its peer group of 51,551 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.1 Bluesky, 0.1 Mastodon, and 0.4 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.1 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (4)

microsoftpatch availablevia msrc
Product: 18977-16820Fixed in: 5.7.2-4
microsoftpatch availablevia msrc
Product: 18902-16823Fixed in: 5.9.5-1
microsoftpatch availablevia msrc
Product: cm1 strongswan 5.7.2-4 on CBL Mariner 1.0Fixed in: 5.7.2-4
microsoftpatch availablevia msrc
Product: cbl2 strongswan 5.9.5-1 on CBL Mariner 2.0Fixed in: 5.9.5-1

Vendor Advisories (2)

redhatCVE-2021-41991Moderate

strongswan: integer overflow when replacing certificates in cache

Oct 18, 2021
microsoft2021-Oct/CVE-2021-41991Important

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.

Oct 12, 2021

References

cert-portal.siemens.com / productcert/pdf/ssa-539476.pdf
PatchThird Party Advisory
github.com / strongswan/strongswan/releases/tag/5.9.4
Third Party Advisory
lists.debian.org / debian-lts-announce/2021/10/msg00014.html
Mailing ListThird Party Advisory
lists.fedoraproject.org / archives/list/package-announce%40lists.fedoraproject.org/message/5FJSATD2R2XHTG4P63GCMQ2N7EWKMME5
lists.fedoraproject.org / archives/list/package-announce%40lists.fedoraproject.org/message/WQSQ3BEC22NF4NCDZVCT4P3Q2ZIAJXGJ
lists.fedoraproject.org / archives/list/package-announce%40lists.fedoraproject.org/message/Y3TQ32JLJOBJDB2EJKSX2PBPB5NFG2D4
debian.org / security/2021/dsa-4989
Third Party Advisory
strongswan.org / blog/2021/10/18/strongswan-vulnerability-%28cve-2021-41991%29.html