CVE-2025-22003 can: ucan: fix out of bound read in strscpy() source
A one-byte out-of-bounds read in the Linux kernel ucan driver allows attackers to potentially disclose adjacent memory contents.
- 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-2025-22003?
CVE-2025-22003 is a medium-severity vulnerability in Linux kernel, published on 3 Apr 2025. 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:
can: ucan: fix out of bound read in strscpy() source
Commit 7fdaf8966aae ("can: ucan: use strscpy() to instead of strncpy()") unintentionally introduced a one byte out of bound read on strscpy()'s source argument (which is kind of ironic knowing that strscpy() is meant to be a more secure alternative :)).
Let's consider below buffers:
dest[len + 1]; /* will be NUL terminated */ src[len]; /* may not be NUL terminated */
When doing:
strncpy(dest, src, len); dest[len] = '\0';
strncpy() will read up to len bytes from src.
On the other hand:
strscpy(dest, src, len + 1);
will read up to len + 1 bytes from src, that is to say, an out of bound read of one byte will occur on src if it is not NUL terminated. Note that the src[len] byte is never copied, but strscpy() still needs to read it to check whether a truncation occurred or not.
This exact pattern happened in ucan.
The root cause is that the source is not NUL terminated. Instead of doing a copy in a local buffer, directly NUL terminate it as soon as usb_control_msg() returns. With this, the local firmware_str[] variable can be removed.
On top of this do a couple refactors:
- ucan_ctl_payload->raw is only used for the firmware string, so rename it to ucan_ctl_payload->fw_str and change its type from u8 to char.
- ucan_device_request_in() is only used to retrieve the firmware string, so rename it to ucan_get_fw_str() and refactor it to make it directly handle all the string termination logic.
Weakness: CWE-125
Which versions are affected by CVE-2025-22003?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2025-22003?
Apply the vendor's patch.
Is CVE-2025-22003 being exploited?
There is no known exploitation of CVE-2025-22003 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as AZL-59826, BELL-CVE-2025-22003, DEBIAN-CVE-2025-22003, GHSA-2648-xh5w-2w3q, ROOT-OS-UBUNTU-2404-CVE-2025-22003, UBUNTU-CVE-2025-22003.