CVE-2025-39682 PoC — tls: fix handling of zero-length records on the rx_list

Source

https://github.com/khoatran107/cve-2025-39682

Associated Vulnerability

Title: tls: fix handling of zero-length records on the rx_list (CVE-2025-39682)
Description:In the Linux kernel, the following vulnerability has been resolved: tls: fix handling of zero-length records on the rx_list Each recvmsg() call must process either - only contiguous DATA records (any number of them) - one non-DATA record If the next record has different type than what has already been processed we break out of the main processing loop. If the record has already been decrypted (which may be the case for TLS 1.3 where we don't know type until decryption) we queue the pending record to the rx_list. Next recvmsg() will pick it up from there. Queuing the skb to rx_list after zero-copy decrypt is not possible, since in that case we decrypted directly to the user space buffer, and we don't have an skb to queue (darg.skb points to the ciphertext skb for access to metadata like length). Only data records are allowed zero-copy, and we break the processing loop after each non-data record. So we should never zero-copy and then find out that the record type has changed. The corner case we missed is when the initial record comes from rx_list, and it's zero length.

Description

A variant of CVE-2024-58239

Readme

# CVE-2025-39682 exploit on kernelCTF mitigation instance
This is also my first (? idk, this is a variant of CVE-2024-58239) 1-day exploit.

Patch: [tls: fix handling of zero-length records on the rx_list](https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/net/tls?id=62708b9452f8eb77513115b17c4f8d1a22ebf843)

This CVE was used in `exp398` and and `exp403`. [kernelCTF spreadsheet](https://docs.google.com/spreadsheets/d/e/2PACX-1vS1REdTA29OJftst8xN5B5x8iIUcxuK6bXdzF8G1UXCmRtoNsoQ9MbebdRdFnj6qZ0Yd7LwQfvYC2oF/pubhtml#).

For folder structures and how to run the exploit, refer to my [CVE-2024-58239 repo](https://github.com/khoatran107/cve-2024-58239).

I modify my previous exploit "a little bit". And it works on the same `mitigation-v4-6.6` instance, with a better success rate.

Success rate: 79/100.

Run on kernelCTF instance:
![image](https://hackmd.io/_uploads/BkgxSYo6xl.png)

Detailed write-up coming later, for both CVEs.

File Snapshot

Remarks

1. It is advised to access via the original source first.

2. Local POC snapshots are reserved for subscribers — if the original source is unavailable, the local mirror is part of the paid plan.

View subscription plans →