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CVE Record

CVE-2024-26603: x86/fpu: Stop relying on userspace for info to fault in xsave buffer

In the Linux kernel, the following vulnerability has been resolved: x86/fpu: Stop relying on userspace for info to fault in xsave buffer Before this change, the expected size of the user space buffer was taken from fx_sw->xstate_size. fx_sw->xstate_size can be changed from user-space, so it is possible construct a sigreturn frame where: * fx_sw->xstate_size is smaller than the size required by valid bits in fx_sw->xfeatures. * user-space unmaps parts of the sigrame fpu buffer so that not all of the buffer required by xrstor is accessible. In this case, xrstor tries to restore and accesses the unmapped area which results in a fault. But fault_in_readable succeeds because buf + fx_sw->xstate_size is within the still mapped area, so it goes back and tries xrstor again. It will spin in this loop forever. Instead, fault in the maximum size which can be touched by XRSTOR (taken from fpstate->user_size). [ dhansen: tweak subject / changelog ]

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

This is a Linux kernel reliability bug on x86 systems. A local user can influence signal-return FPU state handling so the kernel repeatedly retries a failing restore path, potentially causing a CPU hang or denial of service. The bundle does not show data theft, privilege escalation, or remote exploitation.

Executive priority

Patch during the next normal kernel maintenance window, sooner for shared compute or untrusted-user environments. Current evidence supports availability impact, not remote compromise or known exploitation.

Technical view

The bug is in x86 FPU sigreturn handling. The kernel trusted user-controlled fx_sw->xstate_size when faulting in the XSAVE buffer. If xfeatures required more state than xstate_size and part of the buffer was unmapped, XRSTOR could fault and retry indefinitely. The fix faults in fpstate->user_size instead.

Likely exposure

Exposure is most relevant to x86 Linux systems running affected kernel builds listed in the CVE record or downstream vendor kernels without the stable fixes. Internet-facing status is not the main factor; local code execution on the host appears required.

Exploitation context

The provided sources do not show CISA KEV listing or active exploitation. The described condition requires crafted userspace signal-return/FPU state behavior and unmapped memory. Treat it as a local denial-of-service risk unless vendor advisories state otherwise.

Researcher notes

The key trust boundary is sigreturn-supplied fx_sw metadata versus the kernel’s actual maximum XRSTOR-touched user state size. Evidence is limited to the CVE description, Linux stable commits, and a Fedora package notice; no exploit status or CVSS vector is provided.

Mitigation direction

  • Update to a vendor kernel containing the referenced stable Linux fixes.
  • Check Fedora or distribution advisories for backported kernel packages.
  • Prioritize shared, multi-user, CI, hosting, and container-dense x86 systems.
  • If updates are delayed, monitor for local kernel hangs or repeated fault-loop symptoms.

Validation and detection

  • Inventory x86 Linux hosts and record kernel versions.
  • Compare installed kernels against vendor advisories and the referenced stable commits.
  • Confirm distribution security updates include CVE-2024-26603 or equivalent backport notes.
  • After updating, reboot into the fixed kernel and verify the running version.
Prepared
Confidence
medium
Sources
8

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

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ATT&CK lookup starting points

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CVE-2024-26603 mapping review

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
3Timeline events
2ADP providers
7Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: noTechnical Impact: partial

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
other:ssvc
CVECVE Program Container

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinuxfcb3635f5018e53024c6be3c3213737f469f74ff, fcb3635f5018e53024c6be3c3213737f469f74ff, fcb3635f5018e53024c6be3c3213737f469f74ff, fcb3635f5018e53024c6be3c3213737f469f74ff, fcb3635f5018e53024c6be3c3213737f469f74ffunaffected
LinuxLinux5.14, 0, 5.15.150, 6.1.79, 6.6.18, 6.7.6, 6.8affected
Weakness

CWE details

No CWE listed

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