CVE-2026-52956: Linux Ceph Out-of-Bounds Read Denial of Service

Technical summary

CVE-2026-52956 is an out-of-bounds read vulnerability in the Linux kernel's libceph library, specifically in the __ceph_x_decrypt() function. During decryption, the function interprets a portion of the buffer as a ceph_x_encrypt_header structure and accesses its magic field without first verifying that the buffer contains sufficient data to hold this structure. The ciphertext_len parameter represents only the encrypted data length and may be smaller than the ceph_x_encrypt_header size. Specially crafted FRAME_TAG_AUTH_REPLY_MORE messages with minimal ciphertext (8 bytes or fewer) can trigger an out-of-bounds memory access. The vulnerability is a CWE-125 (Out-of-bounds Read) issue.

Business impact

Denial of service is the primary impact. A remote attacker with network access to a Ceph cluster can send malformed authentication messages that crash daemons or services relying on Ceph authentication, disrupting storage infrastructure and cluster operations. Organizations relying on Ceph for production storage, virtualization backends, or container orchestration platforms may experience service interruptions. The attack requires no authentication or user interaction, making it a direct threat to availability.

Affected systems

The Linux kernel is affected across all versions containing the vulnerable libceph code. This impacts systems running Ceph cluster components (monitors, OSDs, managers) and any Linux systems with Ceph client libraries for storage access. Kubernetes clusters using Ceph for persistent volume provisioning, OpenStack deployments with Ceph backends, and dedicated Ceph storage appliances based on Linux kernels are at risk. Verify your specific Linux distribution's kernel version against vendor advisories for precise affected version ranges.

Exploitability

Exploitability is high due to the network-accessible attack vector, lack of required privileges, and absence of user interaction. An attacker need only send a crafted Ceph protocol message over the network; no authentication to the Ceph cluster is necessary to trigger the crash. However, the attacker must have network connectivity to a Ceph service port. Exploitation results in denial of service rather than code execution, limiting the overall damage scope but making it an effective disruption tactic.

Remediation

Apply security updates to the Linux kernel that include the bounds-checking fix in __ceph_x_decrypt(). The patch adds validation to ensure the decrypted plaintext is large enough to represent at least the ceph_x_encrypt_header structure before accessing the magic field. Verify against your Linux distribution's security advisory for patched kernel versions and apply via standard kernel update mechanisms. For systems where immediate patching is delayed, restrict network access to Ceph ports to trusted networks as a temporary mitigation.

Patch guidance

Check your Linux distribution's security advisory for kernel updates addressing CVE-2026-52956. Red Hat, Ubuntu, Debian, and other major distributions will release patched kernel versions through their respective channels. For enterprise systems, align kernel updates with your change management process. Validate that patched kernels are available and tested in your environment before rolling out across production Ceph infrastructure. Monitor vendor advisories for specific version numbers and release timelines.

Detection guidance

Monitor system logs for kernel panic or oops messages originating from ceph or libceph components, particularly involving __ceph_x_decrypt() or authentication code paths. Network-based detection is difficult without decrypting Ceph traffic, but anomalously short or malformed Ceph protocol frames arriving at cluster ports may warrant investigation. Implement alerting on unexpected Ceph service restarts or crashes. For forensic analysis, examine kernel core dumps and system logs from affected nodes to correlate timeline and message sources.

Why prioritize this

While the CVSS score of 7.5 (High) reflects network accessibility and denial of service severity, prioritization depends on your infrastructure. Organizations operating Ceph clusters should treat this as high priority due to direct threat to storage availability. Organizations not using Ceph or running only client-side library usage without exposed daemons can deprioritize relative to other kernel vulnerabilities. The lack of KEV status indicates this is not yet weaponized at scale, offering a window to patch proactively.

Risk score, explained

The CVSS 3.1 score of 7.5 HIGH reflects CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H. The network attack vector (AV:N) and low complexity (AC:L) indicate ease of exploitation. No privilege requirement (PR:N) and no user interaction (UI:N) further raise the score. Confidentiality and integrity are unaffected (C:N/I:N), but availability impact is high (A:H) due to denial of service. The score does not capture likelihood of actual exploitation or business context, so combine it with your Ceph deployment footprint and network exposure when setting internal risk levels.

Frequently asked questions