The Linux kernel's tls_decrypt_sg() function advances the msg_iter iterator when mapping user pages for the optimistic TLS 1.3 zero-copy path. If the decrypted record is not unpadded application data, tls_decrypt_sw() retries decryption into a kernel skb but leaves the iterator advanced. This leads to a subsequent copy operation overwriting decrypted bytes beyond the returned length in the caller's iovecs during recvmsg(). A TLS peer can trigger this behavior after the receiver enables TLS_RX_EXPECT_NO_PAD. The fix reverts the iterator by the number of bytes consumed before retrying without zero-copy and includes a self-test to ensure recvmsg() does not overwrite beyond the returned length.

A TLS peer can trigger the vulnerability to cause recvmsg() to overwrite decrypted data beyond the expected buffer length, potentially leading to memory corruption or data integrity issues in the receiving process. No known exploits in the wild have been reported. The impact is limited to scenarios where TLS_RX_EXPECT_NO_PAD is enabled and the TLS 1.3 optimistic zero-copy path is used.

A fix has been implemented in the Linux kernel to restore the msg_iter iterator before retrying decryption without zero-copy, preventing overwrites beyond the returned length. Users should apply the official kernel update containing this fix. Since this is a kernel-level vulnerability, updating to the patched kernel version is the recommended remediation. Patch status is not explicitly confirmed here; check the vendor or kernel mailing list advisories for the exact fixed versions and update accordingly.