CVE-2025-39748
Unknown Unknown - Not Provided
BaseFortify

Publication date: 2025-09-11

Last updated on: 2026-04-18

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: bpf: Forget ranges when refining tnum after JSET Syzbot reported a kernel warning due to a range invariant violation on the following BPF program. 0: call bpf_get_netns_cookie 1: if r0 == 0 goto <exit> 2: if r0 & Oxffffffff goto <exit> The issue is on the path where we fall through both jumps. That path is unreachable at runtime: after insn 1, we know r0 != 0, but with the sign extension on the jset, we would only fallthrough insn 2 if r0 == 0. Unfortunately, is_branch_taken() isn't currently able to figure this out, so the verifier walks all branches. The verifier then refines the register bounds using the second condition and we end up with inconsistent bounds on this unreachable path: 1: if r0 == 0 goto <exit> r0: u64=[0x1, 0xffffffffffffffff] var_off=(0, 0xffffffffffffffff) 2: if r0 & 0xffffffff goto <exit> r0 before reg_bounds_sync: u64=[0x1, 0xffffffffffffffff] var_off=(0, 0) r0 after reg_bounds_sync: u64=[0x1, 0] var_off=(0, 0) Improving the range refinement for JSET to cover all cases is tricky. We also don't expect many users to rely on JSET given LLVM doesn't generate those instructions. So instead of improving the range refinement for JSETs, Eduard suggested we forget the ranges whenever we're narrowing tnums after a JSET. This patch implements that approach.
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Meta Information
Published
2025-09-11
Last Modified
2026-04-18
Generated
2026-05-06
AI Q&A
2025-09-11
EPSS Evaluated
2026-05-05
NVD
CVE-2025-39748
Affected Vendors & Products
Showing 3 associated CPEs
Vendor Product Version / Range
linux linux_kernel From 5.15.160 (inc) to 5.16 (inc)
linux linux_kernel From 5.15.160 (inc) to 5.16 (inc)
linux linux_kernel From 5.15.160 (inc) to 5.16 (inc)
Helpful Resources
Exploitability
CWE
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CWE ID Description
CWE-NVD-CWE-noinfo
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AI Powered Q&A
Can you explain this vulnerability to me?

This vulnerability is in the Linux kernel's BPF verifier related to how it refines register value ranges after a JSET (jump if bits set) instruction. The verifier incorrectly handles an unreachable code path due to sign extension issues, leading to inconsistent bounds on a register. Instead of improving the complex range refinement for JSET, the fix was to forget the ranges when narrowing tnums after a JSET instruction to avoid the inconsistency.


How can this vulnerability impact me? :

The vulnerability causes the BPF verifier to walk through unreachable code paths and produce inconsistent register bounds, which could potentially lead to kernel warnings or instability when running certain BPF programs. However, since the problematic path is unreachable at runtime and LLVM does not generate JSET instructions, the practical impact is expected to be minimal.


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