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No exploitation reportedFix available

CVE-2021-41991

No exploitation reported by the sources we read.

  • Published2021-10-18
  • WeaknessCWE-190

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

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.

Timeline

dates in UTC
  1. 2021-10-1814:15CVE publishedNVD

Observed activity

isMalicious corpus · updated 2026-10-23 18:48 UTC
Indicators tagged with this CVE, per day0 indicators over 7 days
Block these indicators
  • Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2021-41991?format=txt
  • CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-41991?format=csv
  • TAXII collection of exploited CVEs
  • The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD
Debian debian linux
BranchAffectedFixed in
9.0= 9.0no fix published
10.0= 10.0no fix published
11.0= 11.0no fix published
Fedoraproject fedora
BranchAffectedFixed in
33.x= 33no fix published
34.x= 34no fix published
35.x= 35no fix published
Siemens cp 1543-1 firmwareversion to verify
BranchAffectedFixed in
—all versionsno fix published

22 more products in the sources.

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Vendor advisories

  • ICSA-25-259-03 CISA41 known affected

    Siemens SIMATIC NET CP, SINEMA and SCALANCE

    Siemens Siemens RUGGEDCOM RM1224 LTE(4G) EU (6GK6108-4AM00-2BA2): <V7.1 · Siemens Siemens SCALANCE M874-3 (6GK5874-3AA00-2AA2): <V7.1 · Siemens Siemens SCALANCE M876-3 (EVDO) (6GK5876-3AA02-2BA2): <V7.1 · +38 more

Full record on NVD

Fix

  1. Mitigation from the vendor CISA ICSA-25-259-03 · 41 productsSiemens has identified the following specific workarounds and mitigations users can apply to reduce risk:
  2. Mitigation from the vendor CISA ICSA-25-259-03 · 41 productsRUGGEDCOM RM1224 LTE(4G) EU (6GK6108-4AM00-2BA2), RUGGEDCOM RM1224 LTE(4G) NAM (6GK6108-4AM00-2DA2), SCALANCE M804PB (6GK5804-0AP00-2AA2), SCALANCE M812-1 ADSL-Router (Annex A) (6GK5812-1AA00-2AA2), SCALANCE M812-1 ADSL-Router (Annex B) (6GK5812-1BA00-2AA2), SCALANCE M816-1 ADSL-Router (Annex A) (6…
  3. Mitigation from the vendor CISA ICSA-25-259-03 · 41 products(CVE-2021-41991) SIMATIC CP 1242-7 V2 (6GK7242-7KX31-0XE0), SIMATIC CP 1243-1 (6GK7243-1BX30-0XE0), SIMATIC CP 1243-7 LTE EU (6GK7243-7KX30-0XE0), SIMATIC CP 1243-7 LTE US (6GK7243-7SX30-0XE0), SIMATIC CP 1243-8 IRC (6GK7243-8RX30-0XE0), SIMATIC CP 1542SP-1 (6GK7542-6UX00-0XE0), SIMATIC CP 1543-1 (…
  4. Mitigation from the vendor CISA ICSA-25-259-03 · 41 products(CVE-2021-41991) SIMATIC CP 1542SP-1 (6GK7542-6UX00-0XE0), SIMATIC CP 1542SP-1 IRC (6GK7542-6VX00-0XE0), SIMATIC CP 1543SP-1 (6GK7543-6WX00-0XE0), SIPLUS ET 200SP CP 1542SP-1 IRC TX RAIL (6AG2542-6VX00-4XE0), SIPLUS ET 200SP CP 1543SP-1 ISEC (6AG1543-6WX00-7XE0), SIPLUS ET 200SP CP 1543SP-1 ISEC TX…
  5. Mitigation from the vendor CISA ICSA-25-259-03 · 41 products(CVE-2021-41991) SIMATIC CP 1242-7 V2 (6GK7242-7KX31-0XE0), SIMATIC CP 1243-1 (6GK7243-1BX30-0XE0), SIMATIC CP 1243-7 LTE EU (6GK7243-7KX30-0XE0), SIMATIC CP 1243-7 LTE US (6GK7243-7SX30-0XE0), SIMATIC CP 1243-8 IRC (6GK7243-8RX30-0XE0), SIPLUS NET CP 1242-7 V2 (6AG1242-7KX31-7XE0), SIPLUS S7-1200 …
  6. Mitigation from the vendor CISA ICSA-25-259-03 · 41 products(CVE-2021-41991) SIMATIC CP 1545-1 (6GK7545-1GX00-0XE0): Update to V1.1 or later version

Advisories and patches

Detection

Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof-of-concept repositories
none listed
PoC-in-GitHub

Sources

  • NVDCVSS 3.17.5read 2026-10-23
  • NVDCVSS 2.05read 2026-10-23
  • NVDweakness (CWE)CWE-190read 2026-10-23
  • FIRST EPSSEPSS score5.3 %2026-10-22

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Published
2021-10-18
Last Modified
2026-06-17
NVD status
Modified

Frequently asked questions

What is CVE-2021-41991?

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.

Is CVE-2021-41991 actively exploited?

Active exploitation of CVE-2021-41991 has not been confirmed. Its EPSS score was 5.3% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-41991?

CVE-2021-41991 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

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