If a tokio::sync::oneshot channel is closed (via the oneshot::Receiver::close method), a data race may occur if the oneshot::Sender::send method is called while the corresponding oneshot::Receiver is awaited or calling try_recv.

When these methods are called concurrently on a closed channel, the two halves of the channel can concurrently access a shared memory location, resulting in a data race. This has been observed to cause memory corruption.

Note that the race only occurs when both halves of the channel are used after the Receiver half has called close. Code where close is not used, or where the Receiver is not awaited and try_recv is not called after calling close, is not affected.

See tokio#4225 for more details.

Impact

Due to a non-constant-time implementation, information about the private key is leaked through timing information which is observable over the network. An attacker may be able to use that information to recover the key.

Patches

No patch is yet available. The crypto-bigint migration (RustCrypto/RSA#394) did not close this. Tracking is RustCrypto/RSA#626 (padding still not constant-time). Implicit rejection work is in RustCrypto/RSA#680; default-path blinding is in RustCrypto/RSA#702.

Still affected as of 2026-09-12: rsa 0.9.10 (latest stable) and rsa 0.10.0-rc.18 (latest). patched = [] is intentional.

Workarounds

Avoid using the rsa crate in settings where attackers can observe timing, for example over the network. Local use on a non-compromised computer is fine.

References

This vulnerability was discovered as part of the "Marvin Attack", which revealed several implementations of RSA including OpenSSL had not properly mitigated timing sidechannel attacks.