How severe is CVE-2021-41991?

CVE-2021-41991 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2021-41991 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 5% (91st percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-41991?

CVE-2021-41991 primarily affects Strongswan. In total, 29 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-41991?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2021-41991 published?

CVE-2021-41991 was published on 2021-10-18 and last updated on 2026-06-17.

CVE-2021-41991

CVE-2021-41991 is a high-severity vulnerability in Strongswan with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-190.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v2: 5.0
EPSS exploit prediction: 5% (91st percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-190
Affected product: Strongswan
Published: 2021-10-18
Last modified: 2026-06-17

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.

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.
How severe is CVE-2021-41991?: CVE-2021-41991 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2021-41991 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 5% (91st percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-41991?: CVE-2021-41991 primarily affects Strongswan. In total, 29 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-41991?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2021-41991 published?: CVE-2021-41991 was published on 2021-10-18 and last updated on 2026-06-17.

References

Affected products (29)

cpe:2.3:a:strongswan:strongswan:*:*:*:*:*:*:*:*
cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:*
cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:*
cpe:2.3:o:debian:debian_linux:11.0:*:*:*:*:*:*:*
cpe:2.3:o:fedoraproject:fedora:33:*:*:*:*:*:*:*
cpe:2.3:o:fedoraproject:fedora:34:*:*:*:*:*:*:*
cpe:2.3:o:fedoraproject:fedora:35:*:*:*:*:*:*:*
cpe:2.3:a:siemens:sinema_remote_connect_server:-:*:*:*:*:*:*:*
cpe:2.3:o:siemens:siplus_et_200sp_cp_1542sp-1_irc_tx_rail_firmware:-:*:*:*:*:*:*:*
cpe:2.3:o:siemens:simatic_cp_1243-1_firmware:-:*:*:*:*:*:*:*
cpe:2.3:o:siemens:simatic_cp_1242-7_gprs_v2_firmware:-:*:*:*:*:*:*:*
cpe:2.3:o:siemens:simatic_net_cp_1243-8_irc_firmware:-:*:*:*:*:*:*:*
cpe:2.3:o:siemens:scalance_sc632-2c_firmware:-:*:*:*:*:*:*:*
cpe:2.3:o:siemens:siplus_et_200sp_cp_1543sp-1_isec_firmware:-:*:*:*:*:*:*:*
cpe:2.3:o:siemens:cp_1543-1_firmware:-:*:*:*:*:*:*:*
cpe:2.3:o:siemens:simatic_net_cp_1545-1_firmware:-:*:*:*:*:*:*:*
cpe:2.3:o:siemens:simatic_cp_1543sp-1_firmware:-:*:*:*:*:*:*:*
cpe:2.3:o:siemens:simatic_net_cp1243-7_lte_eu_firmware:-:*:*:*:*:*:*:*
cpe:2.3:o:siemens:simatic_cp_1243-7_lte\/us_firmware:-:*:*:*:*:*:*:*
cpe:2.3:o:siemens:simatic_cp_1542sp-1_firmware:-:*:*:*:*:*:*:*
cpe:2.3:o:siemens:scalance_sc636-2c_firmware:-:*:*:*:*:*:*:*
cpe:2.3:o:siemens:simatic_cp_1542sp-1_irc_firmware:-:*:*:*:*:*:*:*
cpe:2.3:o:siemens:scalance_sc642-2c_firmware:-:*:*:*:*:*:*:*
cpe:2.3:o:siemens:scalance_sc646-2c_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:scalance_sc622-2c_firmware:-:*:*:*:*:*:*:*
cpe:2.3:o:siemens:siplus_s7-1200_cp_1243-1_rail_firmware:-:*:*:*:*:*:*:*
cpe:2.3:o:siemens:siplus_s7-1200_cp_1243-1_firmware:-:*:*:*:*:*:*:*
cpe:2.3:o:siemens:siplus_net_cp_1543-1_firmware:-:*:*:*:*:*:*:*
cpe:2.3:o:siemens:siplus_et_200sp_cp_1543sp-1_isec_tx_rail_firmware:-:*:*:*:*:*:*:*

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