title: Large RSA keys can cause high CPU usage in crypto/tls
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.
problem types: CWE-400: Uncontrolled Resource Consumption
affected:
{
vendor: Go standard library
product: crypto/tls
collectionURL: https://pkg.go.dev
packageName: crypto/tls
versions:
version: 0, lessThan: 1.19.12, status: affected, versionType: semver
version: 1.20.0-0, lessThan: 1.20.7, status: affected, versionType: semver
version: 1.21.0-0, lessThan: 1.21.0-rc.4, status: affected, versionType: semver
programRoutines:
name: Conn.verifyServerCertificate
name: Conn.processCertsFromClient
name: Conn.Handshake
name: Conn.HandshakeContext
name: Conn.Read
name: Conn.Write
name: Dial
name: DialWithDialer
name: Dialer.Dial
name: Dialer.DialContext
defaultStatus: unaffected
}