Infinite loop in strongSwan - CVE-2026-35328
Published: September 22, 2026
Vulnerability identifier: #VU151578
CSH Severity: Medium
CVSS v4: 8.7 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-35328
CWE-ID: CWE-835
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to cause a denial of service.
The vulnerability exists due to an incorrect loop condition in libtls tls_server.c::process_client_hello() when processing a supported_versions TLS extension with a length that is not a multiple of two bytes. A remote attacker can send a crafted ClientHello message to exhaust the daemon's thread pool and cause a denial of service.
The extension is parsed even when TLS 1.3 is disabled.
Affected software
strongSwan
Debian Linux
Fedora
strongswan (Debian package)
strongswan
Debian Linux
Fedora
strongswan (Debian package)
strongswan
How to mitigate CVE-2026-35328
Install security update from vendor's website.
strongSwan - update to 6.0.6
strongswan (Debian package) - addressed in versions 5.9.8-5+deb12u4, 6.0.1-6+deb13u5
strongswan - addressed in versions 6.0.6-1.el8, 6.0.6-1.el9, 6.0.6-1.el10_3, 6.0.6-2.fc44, 6.0.6-3.fc43, 6.0.7-2.fc43
strongswan (Debian package) - addressed in versions 5.9.8-5+deb12u4, 6.0.1-6+deb13u5
strongswan - addressed in versions 6.0.6-1.el8, 6.0.6-1.el9, 6.0.6-1.el10_3, 6.0.6-2.fc44, 6.0.6-3.fc43, 6.0.7-2.fc43