CVE-2025-38488 smb: client: fix use-after-free in crypt_message when using async crypto
A use-after-free in the Linux kernel SMB client causes crashes when hardware crypto accelerators are used, requiring a patch to restore async handling.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-38488?
CVE-2025-38488 is a critical use after free vulnerability in Debian Debian Linux, published on 28 Jul 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
smb: client: fix use-after-free in crypt_message when using async crypto
The CVE-2024-50047 fix removed asynchronous crypto handling from crypt_message(), assuming all crypto operations are synchronous. However, when hardware crypto accelerators are used, this can cause use-after-free crashes:
crypt_message() // Allocate the creq buffer containing the req creq = smb2_get_aead_req(..., &req);
// Async encryption returns -EINPROGRESS immediately rc = enc ? crypto_aead_encrypt(req) : crypto_aead_decrypt(req);
// Free creq while async operation is still in progress kvfree_sensitive(creq, ...);
Hardware crypto modules often implement async AEAD operations for performance. When crypto_aead_encrypt/decrypt() returns -EINPROGRESS, the operation completes asynchronously. Without crypto_wait_req(), the function immediately frees the request buffer, leading to crashes when the driver later accesses the freed memory.
This results in a use-after-free condition when the hardware crypto driver later accesses the freed request structure, leading to kernel crashes with NULL pointer dereferences.
The issue occurs because crypto_alloc_aead() with mask=0 doesn't guarantee synchronous operation. Even without CRYPTO_ALG_ASYNC in the mask, async implementations can be selected.
Fix by restoring the async crypto handling: - DECLARE_CRYPTO_WAIT(wait) for completion tracking - aead_request_set_callback() for async completion notification - crypto_wait_req() to wait for operation completion
This ensures the request buffer isn't freed until the crypto operation completes, whether synchronous or asynchronous, while preserving the CVE-2024-50047 fix.
Weakness: CWE-416
Which versions are affected by CVE-2025-38488?
It affects 2 products.
Products include Debian Debian Linux, Linux kernel.
How do I fix CVE-2025-38488?
Apply the vendor's patch.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2025-38488 being exploited?
There is no known exploitation of CVE-2025-38488 in the wild and no public exploit code.
Other vulnerabilities in Debian Debian Linux
Sources
Also known as AZL-73458, BELL-CVE-2025-38488, DEBIAN-CVE-2025-38488, GHSA-8gh3-6693-hwj4, ROOT-OS-DEBIAN-11-CVE-2025-38488, ROOT-OS-DEBIAN-12-CVE-2025-38488 and 3 more.