Description
PuTTY 0.68 through 0.73 has an Observable Discrepancy leading to an information leak in the algorithm negotiation. This allows man-in-the-middle attackers to target initial connection attempts (where no host key for the server has been cached by the client).
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 | putty | 0.74-1 | — |
| Debian 13 | putty | 0.74-1 | — |
| Debian 12 | putty | 0.74-1 | — |
| Debian 10 | putty | 0.74-1+deb11u1~deb10u1 | DLA-3794-1 |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 20.04 LTS | putty | No fix yet | — |
| Ubuntu 18.04 LTS | putty | No fix yet | — |
| Ubuntu 16.04 LTS | putty | No fix yet | — |
Alpine
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine v3.24 | putty | 0.74-r0 | — |
| Alpine v3.23 | putty | 0.74-r0 | — |
| Alpine v3.22 | putty | 0.74-r0 | — |
| Alpine v3.21 | putty | 0.74-r0 | — |
| Alpine v3.20 | putty | 0.74-r0 | — |
Show 11 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine v3.19 | putty | 0.74-r0 | — |
| Alpine v3.18 | putty | 0.74-r0 | — |
| Alpine v3.17 | putty | 0.74-r0 | — |
| Alpine v3.16 | putty | 0.74-r0 | — |
| Alpine v3.15 | putty | 0.74-r0 | — |
| Alpine v3.14 | putty | 0.74-r0 | — |
| Alpine v3.13 | putty | 0.74-r0 | — |
| Alpine v3.12 | putty | 0.74-r0 | — |
| Alpine v3.11 | putty | 0.74-r0 | — |
| Alpine v3.10 | putty | 0.74-r0 | — |
| Alpine v3.9 | putty | 0.74-r0 | — |
Advisories 2
- DLA-3794-1 putty - security update Debian Security (DSA / DLA) · Mar 9, 2026
- WID-SEC-2024-0975 PuTTY: Schwachstelle ermöglicht Umgehen von Sicherheitsvorkehrungen BSI CERT-Bund (WID) · Apr 25, 2024
References
- https://www.chiark.greenend.org.uk/~sgtatham/putty/changes.html
- https://lists.tartarus.org/pipermail/putty-announce/
- https://www.fzi.de/en/news/news/detail-en/artikel/fsa-2020-2-ausnutzung-eines-informationslecks-fuer-gezielte-mitm-angriffe-auf-ssh-clients/
- FEDORA-2020-35442ce9b7 vendor-advisory
- FEDORA-2020-f4dba093f1 vendor-advisory
- https://security.netapp.com/advisory/ntap-20200717-0003/
- [debian-lts-announce] 20240425 [SECURITY] [DLA 3794-1] putty security update mailing-list