# CVE-2026-99274: smb: client: fix fiemap wild read on empty truncated response

Status: published. Published: 2026-11-07. Updated: 2026-11-07.

In the Linux kernel, the following vulnerability has been resolved:

smb: client: fix fiemap wild read on empty truncated response

smb3_fiemap() treats -E2BIG from SMB2_ioctl() as a truncated range blob
and loops for the next chunk. If the server reports
STATUS_BUFFER_OVERFLOW with OutputCount == 0, SMB2_ioctl() returns
-E2BIG with out_data == NULL and out_data_len == 0, and the existing
length checks accept the empty result. The loop then evaluates

	next = out_data[num - 1].file_offset + ...

with num == 0, reading 16 bytes before NULL.

Reject a truncated range blob that contains no range, so the resume
offset is never computed from an empty response. Also require the last
range in a truncated blob to advance the resume offset without
overflowing, and to stay within the requested range; a malicious or
broken server could otherwise make no progress or underflow len and loop
forever. Free the previous response buffer before retrying.

Reproduced on 6.6.87.2 with a malicious SMB2 server that answers
FSCTL_QUERY_ALLOCATED_RANGES with STATUS_BUFFER_OVERFLOW and
OutputCount == 0; an FS_IOC_FIEMAP ioctl on the mount oopses in
cifs_fiemap() with CR2 = fffffffffffffff8. The code path is unchanged
on mainline.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- Linux / Linux: ≥ 2f3ebaba13cebd8badfb9aed31c0cf3cc82eb4f4; < 4a426ca5be7e3dedbe76575b967db04fbf01136f (affected, git); ≥ 2f3ebaba13cebd8badfb9aed31c0cf3cc82eb4f4; < 31f6dbb29fe17fa9595c7e8b19fd92915b03a4ca (affected, git); ≥ 2f3ebaba13cebd8badfb9aed31c0cf3cc82eb4f4; < f5baa17a0f316c235d61623ac8e8fb32c2b3c0cc (affected, git). Source: CNA: Linux
- Linux / Linux: 5.2 (affected); ≥ 0; < 5.2 (unaffected, semver); ≥ 6.18.61; ≤ 6.18.* (unaffected, semver); ≥ 7.3.2; ≤ 7.3.* (unaffected, semver); ≥ 7.4-rc1; ≤ * (unaffected, original_commit_for_fix). Source: CNA: Linux

## Severity and prioritization

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: Not available

- Weaknesses: Not reported

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://git.kernel.org/stable/c/4a426ca5be7e3dedbe76575b967db04fbf01136f (CNA: Linux)

- https://git.kernel.org/stable/c/31f6dbb29fe17fa9595c7e8b19fd92915b03a4ca (CNA: Linux)

- https://git.kernel.org/stable/c/f5baa17a0f316c235d61623ac8e8fb32c2b3c0cc (CNA: Linux)

## Provenance

- CNA: Linux: https://www.cve.org/CVERecord?id=CVE-2026-99274; retrieved 2026-11-07; source updated 2026-11-07

Revision: c21dd7abc902b91d6dfcca7b691f79be985bbba8d422b9896c8e7930d3c6c3e5

Canonical: https://y2.dev/cve/CVE-2026-99274

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