For those of you who haven't seen, CVE-2024-31497 in the PuTTY tool was announced in the past day. If you're using a NIST P521 ECDSA key and have ever used it with affected versions of PuTTY, you should remove its access everywhere and consider it potentially disclosed. Details here:
https://www.chiark.greenend.org.uk/~sgtatham/putty/wishlist/vuln-p521-bias.h...
The key type is generally listed as the first field in the corresponding public key file, or in each line of an authorized_keys entry, including those you may have set for your account in our Gerrit server (review.opendev.org). If the type is listed as ecdsa-sha2-nistp521 or sk-ecdsa-sha2-nistp521@openssh.com then it's been put at risk if ever used with PuTTY versions 0.68 through 0.80.
On a related note, since I wanted to see how popular that key type is among our Gerrit users, I ran some quick statistics. Of the 36976 accounts created there to date, 19888 of them have SSH keys authorized. There are 35057 total authorized keys, which means accounts with SSH keys average 1.76 keys per account. Out of those keys, 44 claim to be NIST P521 type (0.13%) used by 41 different accounts (0.20% of accounts with keys, 0.11% of all accounts).
Here's a breakdown of the most popular types for keys authorized in our Gerrit:
95% ssh-rsa 3.2% ssh-ed25519 1.4% ssh-dss 0.38% ecdsa-sha2-nistp256 0.25% ssh-dsa 0.13% ecdsa-sha2-nistp521 0.023% ecdsa-sha2-nistp384
So as you can see, the key type potentially impacted by CVE-2024-31497 isn't all that popular in our circles, but it's definitely nonzero.