Description
The TLS stack in Mono before 3.12.1 allows man-in-the-middle attackers to conduct message skipping attacks and consequently impersonate clients by leveraging missing handshake state validation, aka a "SMACK SKIP-TLS" issue.
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 | mono | 3.2.8+dfsg-10 | — |
| Debian 13 | mono | 3.2.8+dfsg-10 | — |
| Debian 12 | mono | 3.2.8+dfsg-10 | — |
| Debian 7 | mono | 2.10.8.1-8+deb7u1 | DSA-3202-1 |
| Debian 6.0 | mono | 2.6.7-5.1+deb6u1 | DLA-176-1 |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 14.04 LTS | mono | 3.2.8+dfsg-4ubuntu1.1 | USN-2547-1 |
Advisories 3
- USN-2547-1 mono vulnerabilities Ubuntu Security Notices (USN) · Apr 22, 2026
- DSA-3202-1 mono - security update Debian Security (DSA / DLA) · Mar 9, 2026
- DLA-176-1 mono - security update Debian Security (DSA / DLA) · Mar 9, 2026
References
- USN-2547-1 vendor-advisory
- https://mitls.org/pages/attacks/SMACK#skip
- https://bugzilla.redhat.com/show_bug.cgi?id=1202869
- 73253 vdb-entry
- [oss-security] 20150317 Re: Mono TLS vulnerabilities mailing-list
- http://www.mono-project.com/news/2015/03/07/mono-tls-vulnerability/
- DSA-3202 vendor-advisory
- https://github.com/mono/mono/commit/1509226c41d74194c146deb173e752b8d3cdeec4