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.
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 14 | strongswan | 5.9.4-1 | — |
| Debian 13 | strongswan | 5.9.4-1 | — |
| Debian 12 | strongswan | 5.9.4-1 | — |
| Debian 11 | strongswan | 5.9.1-1+deb11u1 | DSA-4989-1 |
| Debian 10 | strongswan | 5.7.2-1+deb10u1 | DSA-4989-1 |
Show 1 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 9 | strongswan | 5.5.1-4+deb9u5 | DLA-2788-1 |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 22.04 LTS | strongswan | 5.9.1-1ubuntu3.1 | — |
| Ubuntu 20.04 LTS | strongswan | 5.8.2-1ubuntu3.3 | USN-5111-1 |
| Ubuntu 18.04 LTS | strongswan | 5.6.2-1ubuntu2.7 | USN-5111-1 |
Show 8 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu Pro FIPS 20.04 LTS | strongswan | No fix yet | — |
| Ubuntu Pro FIPS 18.04 LTS | strongswan | No fix yet | — |
| Ubuntu Pro FIPS 16.04 LTS | strongswan | No fix yet | — |
| Ubuntu Pro FIPS-updates 20.04 LTS | strongswan | 5.8.2-1ubuntu3.fips.3.3.1 | — |
| Ubuntu Pro FIPS-updates 18.04 LTS | strongswan | 5.6.2-1ubuntu2.fips.2.7.1 | — |
| Ubuntu Pro FIPS-updates 16.04 LTS | strongswan | 5.3.5-1ubuntu3.fips.3.8.2 | — |
| Ubuntu Pro 16.04 LTS | strongswan | 5.3.5-1ubuntu3.8+esm1 | USN-5111-2 |
| Ubuntu Pro 14.04 LTS | strongswan | 5.1.2-0ubuntu2.11+esm1 | USN-5111-2 |
SUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SLES 15 SP3 | strongswan | 5.8.2-11.21.1 | SUSE-SU-2021:3467-1 |
| SLES 15 SP2 | strongswan | 5.8.2-11.21.1 | SUSE-SU-2021:3467-1 |
| SLES 15 SP1 | strongswan | 5.8.2-4.14.2 | SUSE-SU-2021:3469-1 |
| SLES 15 | strongswan | 5.8.2-4.14.2 | SUSE-SU-2021:3469-1 |
| SLES 12 SP5 | strongswan | 5.1.3-26.16.1 | SUSE-SU-2021:3468-1 |
Show 18 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SLES 12 SP4 | strongswan | 5.1.3-26.16.1 | SUSE-SU-2021:3468-1 |
| SLES 12 SP3 | strongswan | 5.1.3-26.16.1 | SUSE-SU-2021:3468-1 |
| SLES 12 SP2 | strongswan | 5.1.3-26.16.1 | SUSE-SU-2021:3468-1 |
| SLES 11 SP4 | strongswan | 4.4.0-6.36.9.1 | SUSE-SU-2021:14827-1 |
| SLES for SAP 15 SP1 | strongswan | 5.8.2-4.14.2 | SUSE-SU-2021:3469-1 |
| SLES for SAP 15 | strongswan | 5.8.2-4.14.2 | SUSE-SU-2021:3469-1 |
| SLES for SAP 12 SP5 | strongswan | 5.1.3-26.16.1 | SUSE-SU-2021:3468-1 |
| SLES for SAP 12 SP4 | strongswan | 5.1.3-26.16.1 | SUSE-SU-2021:3468-1 |
| SLES for SAP 12 SP3 | strongswan | 5.1.3-26.16.1 | SUSE-SU-2021:3468-1 |
| SLE HPC 15 SP1 | strongswan | 5.8.2-4.14.2 | SUSE-SU-2021:3469-1 |
| SLE HPC 15 | strongswan | 5.8.2-4.14.2 | SUSE-SU-2021:3469-1 |
| SUSE OpenStack Cloud Crowbar 9 | strongswan | 5.1.3-26.16.1 | SUSE-SU-2021:3468-1 |
| SUSE OpenStack Cloud Crowbar 8 | strongswan | 5.1.3-26.16.1 | SUSE-SU-2021:3468-1 |
| SUSE OpenStack Cloud 9 | strongswan | 5.1.3-26.16.1 | SUSE-SU-2021:3468-1 |
| SUSE OpenStack Cloud 8 | strongswan | 5.1.3-26.16.1 | SUSE-SU-2021:3468-1 |
| SUSE Linux Enterprise Point of Sale 11 SP3 | strongswan | 4.4.0-6.36.9.1 | SUSE-SU-2021:14827-1 |
| SUSE HPE Helion OpenStack 8 | strongswan | 5.1.3-26.16.1 | SUSE-SU-2021:3468-1 |
| SUSE Enterprise Storage 6 | strongswan | 5.8.2-4.14.2 | SUSE-SU-2021:3469-1 |
openSUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| openSUSE Tumbleweed | strongswan | 5.9.4-1.1 | openSUSE-SU-2024:11655-1 |
| openSUSE Leap 15.3 | strongswan | 5.8.2-11.21.1 | openSUSE-SU-2021:3467-1 |
| openSUSE Leap 15.2 | strongswan | 5.8.2-lp152.2.18.1 | openSUSE-SU-2021:1399-1 |
Alpine
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine v3.24 | strongswan | 5.9.1-r3 | — |
| Alpine v3.23 | strongswan | 5.9.1-r3 | — |
| Alpine v3.22 | strongswan | 5.9.1-r3 | — |
| Alpine v3.21 | strongswan | 5.9.1-r3 | — |
| Alpine v3.20 | strongswan | 5.9.1-r3 | — |
Show 8 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine v3.19 | strongswan | 5.9.1-r3 | — |
| Alpine v3.18 | strongswan | 5.9.1-r3 | — |
| Alpine v3.17 | strongswan | 5.9.1-r3 | — |
| Alpine v3.16 | strongswan | 5.9.1-r3 | — |
| Alpine v3.15 | strongswan | 5.9.1-r3 | — |
| Alpine v3.14 | strongswan | 5.9.1-r2 | — |
| Alpine v3.13 | strongswan | 5.9.1-r1 | — |
| Alpine v3.12 | strongswan | 5.8.4-r3 | — |
Azure Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Azure Linux 2 (CBL-Mariner) | strongswan | 5.9.5-1 | — |
Advisories 14
- USN-5111-2 strongswan vulnerability Ubuntu Security Notices (USN) · Jun 29, 2026
- USN-5111-1 strongswan vulnerabilities Ubuntu Security Notices (USN) · Apr 27, 2026
- DSA-4989-1 strongswan - security update Debian Security (DSA / DLA) · Mar 9, 2026
- DLA-2788-1 strongswan - security update Debian Security (DSA / DLA) · Mar 9, 2026
- SUSE-SU-2021:3468-1 Security update for strongswan SUSE / openSUSE Security Updates · Feb 4, 2026
- openSUSE-SU-2021:1399-1 Security update for strongswan SUSE / openSUSE Security Updates · Feb 4, 2026
- SUSE-SU-2021:14827-1 Security update for strongswan SUSE / openSUSE Security Updates · Feb 4, 2026
- openSUSE-SU-2024:11655-1 strongswan-5.9.4-1.1 on GA media SUSE / openSUSE Security Updates · Feb 4, 2026
- openSUSE-SU-2021:3467-1 Security update for strongswan SUSE / openSUSE Security Updates · Feb 4, 2026
- SUSE-SU-2021:3467-1 Security update for strongswan SUSE / openSUSE Security Updates · Feb 4, 2026
- SUSE-SU-2021:3469-1 Security update for strongswan SUSE / openSUSE Security Updates · Feb 4, 2026
- ICSA-25-259-03 Siemens SIMATIC NET CP, SINEMA and SCALANCE CISA ICS & IT advisories · Sep 16, 2025
- WID-SEC-2024-1024 strongSwan: Mehrere Schwachstellen ermöglichen Denial of Service BSI CERT-Bund (WID) · May 5, 2024
- SSA-539476 SSA-539476: Siemens SIMATIC NET CP, SINEMA and SCALANCE Products Affected by Vulnerabilities in Third-Party Component strongSwan Siemens ProductCERT · Mar 14, 2023
References
- https://github.com/strongswan/strongswan/releases/tag/5.9.4
- https://www.strongswan.org/blog/2021/10/18/strongswan-vulnerability-%28cve-2021-41991%29.html
- DSA-4989 vendor-advisory
- [debian-lts-announce] 20211019 [SECURITY] [DLA 2788-1] strongswan security update mailing-list
- FEDORA-2021-0b37146973 vendor-advisory
- FEDORA-2021-b3df83339e vendor-advisory
- FEDORA-2021-95fab6a482 vendor-advisory
- https://cert-portal.siemens.com/productcert/pdf/ssa-539476.pdf