# CVE-2026-121876: Sandboxed-containers: kernel: systemd-gpt-auto-generator: guest data leakage in confidential computing (sandboxed containers)

Status: published. Published: 2026-11-12. Updated: 2026-11-12.

A flaw was found in the interaction between systemd-gpt-auto-generator and 
confidential computing guest VM images in OpenShift Sandboxed Containers 
(confidential peer pods). systemd-gpt-auto-generator automatically discovers 
and mounts GPT partitions by type GUID at boot with no user confirmation. In 
the confidential computing threat model, where the host/hypervisor is the 
adversary, a malicious host can inject partitions into the guest's virtual 
disk. Most critically, injecting a swap partition causes the guest kernel to 
page out TEE-encrypted memory to a host-controlled block device, breaking the 
confidentiality guarantee of the hardware TEE (AMD SEV-SNP, Intel TDX).

The PodVM images use a GPT-partitioned disk with dm-verity on the root 
partition. However, the roothash= kernel parameter only disables root 
auto-discovery — non-root partitions (swap, /home, /var, /srv, /var/tmp) are 
still auto-discovered and mounted. The generator is shipped unmasked in the 
RHEL systemd-udev subpackage, and no kernel command line parameter in the 
measured UKI addon disables it. Additionally, the PodVM measurement script 
captures PCRs 3, 9, 11, and 12, but not PCR 5 (GPT partition table), so 
partition table modifications are not detected by remote attestation.

## Remediation

- workaround: Add systemd.gpt_auto=0 to the measured kernel command line (UKI addon) to completely 
disable systemd-gpt-auto-generator. Since the PodVM already uses explicit partition 
layout and dm-verity, auto-discovery is unnecessary.

The patches released are using the following mitigation: `systemd.image_policy=root=open`.

Alternative mitigations:
- Disable swap specifically: add systemd.swap=0 to the kernel command line
- Mask the generator in the guest image: 
  ln -sf /dev/null /etc/systemd/system-generators/systemd-gpt-auto-generator
- Include PCR 5 in the PodVM measurement script alongside PCRs 3, 9, 11, 12
- For systemd 254+: set restrictive image policy via systemd.image_policy=root=verity+signed+encrypted+unprotected+absent:swap=absent:home=absent:srv=absent:var=absent:tmp=absent (source: CNA: redhat)

## Affected products and versions

- Red Hat / Red Hat Enterprise Linux 10 (kernel): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 6 (kernel): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 7 (kernel): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 7 (kernel-rt): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 8 (kernel): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 8 (kernel-rt): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 9 (kernel): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 9 (kernel-rt): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat OpenShift Container Platform 4 (openshift/ose-rhel-coreos-8): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat OpenShift Container Platform 4 (openshift/ose-rhel-coreos-9): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat OpenShift Container Platform 5 (openshift/ose-rhel-coreos-9): Version range not reported. Source: CNA: redhat

## Severity and prioritization

- CVSS 3.1: 7.9 (high); CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:N; source: CNA: redhat

- CVSS 3.1: 7.9 (high); CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:N; source: NVD: secalert@redhat.com

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: Not available

- Weaknesses: CWE-359

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://access.redhat.com/security/cve/CVE-2026-121876 (CNA: redhat; vdb-entry, x_refsource_REDHAT)

- https://bugzilla.redhat.com/show_bug.cgi?id=2558210 (CNA: redhat; issue-tracking, x_refsource_REDHAT)

- https://access.redhat.com/security/cve/CVE-2026-121876 (secalert@redhat.com)

- https://bugzilla.redhat.com/show_bug.cgi?id=2558210 (secalert@redhat.com)

## Provenance

- CNA: redhat: https://www.cve.org/CVERecord?id=CVE-2026-121876; retrieved 2026-11-12; source updated 2026-11-12

- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-121876; retrieved 2026-11-12; source updated 2026-11-12

Revision: ee8bf1f329573e6a58a104a84a6e9f11ade256cc7f1f22308f439581d83c4571

Canonical: https://y2.dev/cve/CVE-2026-121876

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