net/sched: cls_u32: validate offshift to prevent shift-out-of-bounds (CVE-2026-74544) | HOL Guard CVE

High · CVSS 7.8CVE-2026-74544

net/sched: cls_u32: validate offshift to prevent shift-out-of-bounds

Answer in brief

CVE-2026-74544 records a High severity (CVSS 7.8) vulnerability in net/sched: cls_u32: validate offshift to prevent shift-out-of-bounds. The current sources do not mark it as known exploited. The current feed maps Linux/Linux (generic), Linux/Linux (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Aug 15, 2026Updated Aug 17, 2026Source checked Sep 30, 2026First seen by HOL Aug 15, 2026Material review Aug 17, 2026

Upstream Advisory

Key facts

Risk: High · CVSS 7.8
Exploitation: Not marked as known exploited
Affected software: 2 mapped packages or products
Fix availability: Available

Why this deserves its current priority

CVSS is 7.8. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps Linux/Linux (generic), Linux/Linux (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
Linux/Linuxgeneric	>=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <313cb9ffc4101a885d791facf4b5ea3d5e06144d \|\| >=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <aef96eead2860cbfa371e4471d4f04412213b958	313cb9ffc4101a885d791facf4b5ea3d5e06144d, aef96eead2860cbfa371e4471d4f04412213b958
Linux/Linuxgeneric	2.6.12	Not reported

Recommended response

Check inventory. Check lockfiles and deployed manifests for Linux/Linux, Linux/Linux.
Review the reported fix. Update Linux/Linux to 313cb9ffc4101a885d791facf4b5ea3d5e06144d if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Aug 15, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Aug 17, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Aug 15, 2026

Sources and claim methodology

Upstream source description

In the Linux kernel, the following vulnerability has been resolved: net/sched: cls_u32: validate offshift to prevent shift-out-of-bounds u32_change() copies the user-provided tc_u32_sel.offshift (unsigned char, 0-255) into the kernel knode object without bounds validation. When a packet later hits u32_classify() with TC_U32_VAROFFSET set, it evaluates `ntohs(offmask & *data) >> offshift` where the left operand is a 16-bit value promoted to a 32-bit int. Any offshift >= 32 is undefined behavior per C11 6.5.7p3, triggerable by an unprivileged user via user/network namespaces. UBSAN: shift-out-of-bounds in net/sched/cls_u32.c:236:43 shift exponent 32 is too large for 32-bit type int Fix this by rejecting offshift >= 16 during filter creation in u32_change().

Quoted source text, attributed separately from HOL analysis.