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Vulnerabilities

Security research · CVE-2026-98869

CVE-2026-98869: bpf: Infer zext_dst based on static register liveness analysis

Published Oct 21, 2026 · catalog updated Oct 21, 2026 · Linux Linux

Last checked Oct 31, 2026. A connected source was read within the last 7 days.

Check if you run it

No confirmed exploitation is on record for CVE-2026-98869. EPSS is 0.17%. Act only if a listed version of Linux Linux is installed.

Gaps on this record

  • No version range is stored. A customer cannot check an installed version against this record.
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.

Same product and reporting

Severity
High—
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.17%
Remediation
Not established
Affected products
linux kernel · vendor Linux Linux

In the Linux kernel, the following vulnerability has been resolved: bpf: Infer zext_dst based on static register liveness analysis As reported in the thread [1], the verifier's 32-bit operations zero extension logic is broken. This logic is responsible for correct semantics of 32-bit operations on s390 architecture. According to BPF semantics, operation is supposed to zero extend the upper half of the register . On s390 the JIT relies on the verifier emitting explicit zero extension before such operations. The verifier attempts to minimize the amount of zero extensions inserted by tracking whether upper halves of the 64-bit registers are ever used. Previously such tracking worked as follows: - bpf_reg_state->subreg_def field was set by do_check_insn() for each operation defining lower but not the upper halves of the register. - Whenever an operation reading the whole register was verified, the verifier checked register's subreg_def and set bpf_insn_aux_data->zext_dst flag as true via a call to mark_insn_zext() function. - After the verification was complete, a special pass bpf_opt_subreg_zext_lo32_rnd_hi32() extended 32-bit operations with bpf_insn_aux_data->zext_dst set as true by adding explicit zero extension. Note that the logic above relies on bpf_reg_state->subreg_def, which is a property of a current verifier state. Before the commit [2] two additional steps happened: - The verifier tracked upper and lower register halves' liveness as flags REG_LIVE_READ{32,64} in bpf_reg_state->live. - The function propagate_liveness() called mark_insn_zext() in order to transfer the knowledge about which registers have their upper halves alive (and thus might require zero extension). The commit [2] removed the two steps described above, hence making possible a situation like below: - The register's upper half is set and is used on some verification path P1 and the register happens not to be marked as precise. - The checkpoint C is created while processing some instruction b

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  • linux kernelversion unspecified
  • vendor Linux Linuxversion unspecified

How to fix CVE-2026-98869

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-98869. EPSS is 0.17%. Act only if a listed version of Linux Linux is installed.

Which versions are affected?

Affected version ranges are not on this record. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

No weakness class is stored. EPSS 0.17%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

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Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Oct 21, 2026 · Linux Kernel CVE

    Detected

    From: Greg Kroah-Hartman Description =========== In the Linux kernel, the following vulnerability has been resolved: bpf: Infer zext_dst based on static register liveness analysis As reported in the thread [1], the verifier's 32-bit operations zero extension logic is broken. This logic is responsible for correct semantics of 32-bit operations on s390 architecture. According to BPF semantics, opera

Sources

  • CVE.orgVulnerability recordCVE-2026-98869

    In the Linux kernel, the following vulnerability has been resolved: bpf: Infer zext_dst based on static register liveness analysis As reported in the thread [1], the verifier's 32-bit operations zero extension logic is broken. This logic is responsible for correct semantics of 32

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-98869

    30-day exploitation probability 0.17%

    first.org
  • Linux Kernel CVEVendor advisoryCVE-2026-98869

    From: Greg Kroah-Hartman Description =========== In the Linux kernel, the following vulnerability has been resolved: bpf: Infer zext_dst based on static register liveness analysis As reported in the thread [1], the verifier's 32-bit operations zero extension logic is broken. This

    git.kernel.org
  • Tenable CVE DatabaseVulnerability recordCVE-2026-98869

    In the Linux kernel, the following vulnerability has been resolved: bpf: Infer zext_dst based on static register liveness analysis As reported in the thread [1], the verifier's 32-bit operations zero extension logic is broken. This logic is responsible for correct semantics of 32-bit operations on s390 architecture. According to BPF semantics, operation is supposed to zero extend the upper half of

    tenable.com

References

Freshness

Last verified in this catalog Oct 31, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.

  • FIRST EPSSOct 28, 2026
  • Tenable CVE DatabaseOct 25, 2026
  • CVE.orgOct 21, 2026
  • Linux Kernel CVEOct 21, 2026