CVE-2025-39748

/// Technical 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

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References