smb: client: reject a tree connect response whose byte count is too small
CVE-2026-89631 · published 11 Sept 2026
How serious is it
- Severity: critical, CVSS score 9.1 out of 10.
- No exploit prediction (EPSS) score yet.
- Not on the CISA list of exploited vulnerabilities.
- No public exploit in Exploit-DB.
Is your app affected by CVE-2026-89631?
Paste this prompt into Claude Code, Cursor or any AI coding tool: it runs a free Shippable scan of your project and fixes what it finds. Built with Lovable, Bolt or v0? Scan your live app. Or upload your package file.
Who is affected
- Linux Linux: cc20c031bb067eb3280a1c4b5c42295093e24863 to < d837645a719151ed392d4d9cab4571c2753dab12, cc20c031bb067eb3280a1c4b5c42295093e24863 to < 2ae219762ebac929bf6ab3473681f10ed566af08, cc20c031bb067eb3280a1c4b5c42295093e24863 to < 3be89e8039a85fa3b6cd5f9dcc4c1459eb356c2d, cc20c031bb067eb3280a1c4b5c42295093e24863 to < 411e484fe71a7f1028de617447edad9cb6d9d68a
- Linux Linux: 2.6.30
How to check
- Find out whether you run the affected product and which version, then compare it with the versions above.
How to fix
Copies a prompt for Claude Code, Cursor or Codex that asks it to check whether you run this product.
- Apply the vendor's update or mitigation from the references below. If there is none yet, limit exposure of the affected service until there is.
- If a vulnerable version was live, check your logs and rotate the secrets that server could read.
The advisory
In the Linux kernel, the following vulnerability has been resolved:
smb: client: reject a tree connect response whose byte count is too small
CIFSTCon() bounds its strnlen() over the byte area with the server's
ByteCount minus two, which for ByteCount 0 or 1 goes negative as an int
and converts to a huge size_t. The later subtraction wraps the __u16
bytes_left, and that is what bounds cifs_strndup_from_utf16(): a bound of
up to 65535 against a ~16 KB cifs_req_poolp object runs off the end of the
slab object, and the bytes reach userspace through tcon->nativeFileSystem
in /proc/fs/cifs/DebugData.
Reject a byte area too small for what the parser consumes. Two bytes is
the least it can consume, and no conformant response carries fewer. The
new trace point is the 129th smb_eio_trace entry, which __mode(byte)
cannot represent, so the attribute goes with it.
Check your whole app
Dependencies are only half of it. Free and read-only: before you push, run npx shippable-dev scan localhost:3000 in your project folder, no account needed. For your live app, you prove it's yours with a one-line tag first.
References
- git.kernel.org/stable/c/d837645a719151ed392d4d9cab4571c2753dab12
- git.kernel.org/stable/c/2ae219762ebac929bf6ab3473681f10ed566af08
- git.kernel.org/stable/c/3be89e8039a85fa3b6cd5f9dcc4c1459eb356c2d
- git.kernel.org/stable/c/411e484fe71a7f1028de617447edad9cb6d9d68a
- git.kernel.org/stable/c/65deb18359341141d37dc86fc7853511be3c87a7
Merged from CVE List. Last updated 26 Oct 2026. All vulnerabilities · RSS · JSON