CVE-2026-31613 smb: client: fix OOB reads parsing symlink error response
A malicious SMB server can trigger out-of-bounds reads in the Linux kernel SMB client, leaking heap memory to userspace via readlink.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-31613?
CVE-2026-31613 is a high-severity memory corruption vulnerability in Linux kernel, published on 24 Apr 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
In the Linux kernel, the following vulnerability has been resolved:
smb: client: fix OOB reads parsing symlink error response
When a CREATE returns STATUS_STOPPED_ON_SYMLINK, smb2_check_message() returns success without any length validation, leaving the symlink parsers as the only defense against an untrusted server.
symlink_data() walks SMB 3.1.1 error contexts with the loop test "p < end", but reads p->ErrorId at offset 4 and p->ErrorDataLength at offset 0. When the server-controlled ErrorDataLength advances p to within 1-7 bytes of end, the next iteration will read past it. When the matching context is found, sym->SymLinkErrorTag is read at offset 4 from p->ErrorContextData with no check that the symlink header itself fits.
smb2_parse_symlink_response() then bounds-checks the substitute name using SMB2_SYMLINK_STRUCT_SIZE as the offset of PathBuffer from iov_base. That value is computed as sizeof(smb2_err_rsp) + sizeof(smb2_symlink_err_rsp), which is correct only when ErrorContextCount == 0.
With at least one error context the symlink data sits 8 bytes deeper, and each skipped non-matching context shifts it further by 8 + ALIGN(ErrorDataLength, 8). The check is too short, allowing the substitute name read to run past iov_len. The out-of-bound heap bytes are UTF-16-decoded into the symlink target and returned to userspace via readlink(2).
Fix this all up by making the loops test require the full context header to fit, rejecting sym if its header runs past end, and bound the substitute name against the actual position of sym->PathBuffer rather than a fixed offset.
Because sub_offs and sub_len are 16bits, the pointer math will not overflow here with the new greater-than.
Weakness: CWE-125
Which versions are affected by CVE-2026-31613?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-31613?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-31613 being exploited?
There is no known exploitation of CVE-2026-31613 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as AZL-83774, BELL-CVE-2026-31613, DEBIAN-CVE-2026-31613, GHSA-3w37-m4pg-q585, ROOT-OS-DEBIAN-12-CVE-2026-31613, ROOT-OS-DEBIAN-13-CVE-2026-31613 and 3 more.