Description
OpenVPN before 2.0.1, when running with "verb 0" and without TLS authentication, does not properly flush the OpenSSL error queue when a client fails certificate authentication to the server and causes the error to be processed by the wrong client, which allows remote attackers to cause a denial of service (client disconnection) via a large number of failed authentication attempts.
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 | openvpn | 2.0.2-1 | — |
| Debian 13 | openvpn | 2.0.2-1 | — |
| Debian 12 | openvpn | 2.0.2-1 | — |
| Debian 3.1 | openvpn | 2.0-1sarge1 | DSA-851-1 |
Advisories 1
- DSA-851-1 openvpn - denial of service Debian Security (DSA / DLA) · Mar 9, 2026
References
- 14605 vdb-entry
- 17103 third-party-advisory
- http://openvpn.net/changelog.html
- MDKSA-2005:145 vendor-advisory
- SUSE-SR:2005:020 vendor-advisory
- DSA-851 vendor-advisory
- 16463 third-party-advisory