VulnerabilityPublished 25 Sep 2026Updated 21 Oct 2026

CVE-2026-98038: Linux kernel · bpf: Keep refcount_acquire nullable for borrowed RCU kptrs

Affects Linux kernelSource CVE Database V5

Not known to be exploited · fixed in dc36739e5cc9f60485418a910b42bc95339218d2 : update Linux kernel when convenient.

Data as of 26 Oct 2026, 13:47 UTC

Severity

Unrated

Rated by Threat Radar · CVSS not yet scored by NVD

EPSS: 0.2% chance of exploitation in 30 days – higher than 11% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in dc36739e5cc9f60485418a910b42bc95339218d2, 85074498228a2500ea8b8039c49cc1ab8ad5328f, 85bfc8b6db43502444c428eaa2de20bdd2fb9064 +1

Exploitation evidence

Disclosed: evidence found.
CVE published 25 Sep 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade Linux kernel to dc36739e5cc9f60485418a910b42bc95339218d2, 85074498228a2500ea8b8039c49cc1ab8ad5328f, 85bfc8b6db43502444c428eaa2de20bdd2fb9064 or 8d19e2cdfba9ba8c8eb6a459cd666bec00a1d2c6.

Affected software

Product	Affected	Fixed in
LinuxLinux	Affected ≥ 1b12171533a9bb23cf6fba7262b479028b65e1e8, < dc36739e5cc9f60485418a910b42bc95339218d2	Fixed in dc36739e5cc9f60485418a910b42bc95339218d2
LinuxLinux	Affected ≥ 1b12171533a9bb23cf6fba7262b479028b65e1e8, < 85074498228a2500ea8b8039c49cc1ab8ad5328f	Fixed in 85074498228a2500ea8b8039c49cc1ab8ad5328f
LinuxLinux	Affected ≥ 1b12171533a9bb23cf6fba7262b479028b65e1e8, < 85bfc8b6db43502444c428eaa2de20bdd2fb9064	Fixed in 85bfc8b6db43502444c428eaa2de20bdd2fb9064
LinuxLinux	Affected ≥ 1b12171533a9bb23cf6fba7262b479028b65e1e8, < 8d19e2cdfba9ba8c8eb6a459cd666bec00a1d2c6	Fixed in 8d19e2cdfba9ba8c8eb6a459cd666bec00a1d2c6
LinuxLinux	Affected =6.8	Fixed in–

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 ]

References

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