# CVE-2026-98038: bpf: Keep refcount_acquire nullable for borrowed RCU kptrs

CVE-2026-98038 is fixed in linux on 1 platform, first by DEBIAN-CVE-2026-98038, released October 2, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-98038
- Priority: Routine
- CVSS: n/a
- EPSS: 0.0022
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Sep 25, 2026
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-98038

## Description

In the Linux kernel, the following vulnerability has been resolved:  bpf: Keep refcount_acquire nullable for borrowed RCU kptrs  bpf_refcount_acquire() is fallible for a borrowed reference because the object may have reached a zero refcount. The verifier therefore keeps KF_RET_NULL on the return value unless the argument is an owning reference.  An RCU-protected load of a local kptr is marked MEM_ALLOC, but it only receives NON_OWN_REF when the pointee contains a graph node. A refcounted object without a graph node consequently looks like an owning reference even though the loaded register has no acquired reference state. If the program drops the last real reference while remaining in the RCU critical section, refcount_inc_not_zero() returns NULL while the verifier treats the result as non-NULL.  Only classify the argument as owning when it is backed by a verifier-tracked reference. This retains the non-NULL return for pointers from bpf_obj_new(), bpf_kptr_xchg(), or an earlier successful acquisition, while requiring a NULL check for borrowed RCU kptrs.  [ kkd: Rewrote commit log ]

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 13.5 (trixie) | 6.12.115-2 | [DEBIAN-CVE-2026-98038](https://patchblox.com/security/data/fix/linux/debian-cve-2026-98038.md) | Oct 2, 2026 |
| Linux | linux Debian 14 | 7.2.7-1 | [DEBIAN-CVE-2026-98038](https://patchblox.com/security/data/fix/linux/debian-cve-2026-98038.md) | Oct 2, 2026 |

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Data as of 2026-11-09T01:18:40Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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