CVE-2024-26996 usb: gadget: f_ncm: Fix UAF ncm object at re-bind after usb ep transport error
A use-after-free vulnerability in the Linux kernel's NCM USB gadget driver allows attackers to cause a system crash or potentially execute code via crafted USB interactions.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2024-26996?
CVE-2024-26996 is a high-severity use after free vulnerability in Linux kernel, published on 1 May 2024. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
usb: gadget: f_ncm: Fix UAF ncm object at re-bind after usb ep transport error
When ncm function is working and then stop usb0 interface for link down, eth_stop() is called. At this piont, accidentally if usb transport error should happen in usb_ep_enable(), 'in_ep' and/or 'out_ep' may not be enabled.
After that, ncm_disable() is called to disable for ncm unbind but gether_disconnect() is never called since 'in_ep' is not enabled.
As the result, ncm object is released in ncm unbind but 'dev->port_usb' associated to 'ncm->port' is not NULL.
And when ncm bind again to recover netdev, ncm object is reallocated but usb0 interface is already associated to previous released ncm object.
Therefore, once usb0 interface is up and eth_start_xmit() is called, released ncm object is dereferrenced and it might cause use-after-free memory.
[function unlink via configfs] usb0: eth_stop dev->port_usb=ffffff9b179c3200 --> error happens in usb_ep_enable(). NCM: ncm_disable: ncm=ffffff9b179c3200 --> no gether_disconnect() since ncm->port.in_ep->enabled is false. NCM: ncm_unbind: ncm unbind ncm=ffffff9b179c3200 NCM: ncm_free: ncm free ncm=ffffff9b179c3200 <-- released ncm
[function link via configfs] NCM: ncm_alloc: ncm alloc ncm=ffffff9ac4f8a000 NCM: ncm_bind: ncm bind ncm=ffffff9ac4f8a000 NCM: ncm_set_alt: ncm=ffffff9ac4f8a000 alt=0 usb0: eth_open dev->port_usb=ffffff9b179c3200 <-- previous released ncm usb0: eth_start dev->port_usb=ffffff9b179c3200 <-- eth_start_xmit() --> dev->wrap() Unable to handle kernel paging request at virtual address dead00000000014f
This patch addresses the issue by checking if 'ncm->netdev' is not NULL at ncm_disable() to call gether_disconnect() to deassociate 'dev->port_usb'. It's more reasonable to check 'ncm->netdev' to call gether_connect/disconnect rather than check 'ncm->port.in_ep->enabled' since it might not be enabled but the gether connection might be established.
Weakness: CWE-416
Which versions are affected by CVE-2024-26996?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2024-26996?
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-2024-26996 being exploited?
There is no known exploitation of CVE-2024-26996 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2024-26996, DEBIAN-CVE-2024-26996, GHSA-2wc3-h48p-9gpq, ROOT-OS-DEBIAN-11-CVE-2024-26996, UBUNTU-CVE-2024-26996.