CVE-2026-68160 in Linux
Summary
by MITRE • 08/10/2026
In the Linux kernel, the following vulnerability has been resolved:
ceph: fix pre-auth out-of-bounds read on snaptrace in ceph_handle_caps()
ceph_handle_caps() reads snap_trace_len from the wire-format ceph_mds_caps header and uses it unconditionally to build a fake end pointer (snaptrace + snaptrace_len) that is later handed to ceph_update_snap_trace() in the CEPH_CAP_OP_IMPORT case:
snaptrace = h + 1; snaptrace_len = le32_to_cpu(h->snap_trace_len); p = snaptrace + snaptrace_len; ... case CEPH_CAP_OP_IMPORT: if (snaptrace_len) {
... if (ceph_update_snap_trace(mdsc, snaptrace, snaptrace + snaptrace_len, false, &realm)) { ... }
ceph_update_snap_trace() then decodes a struct ceph_mds_snap_realm from snaptrace using ceph_decode_need(&p, e, sizeof(*ri), bad) with the attacker-supplied fake end e == snaptrace + snaptrace_len. With snaptrace_len == 0xFFFFFFFF the bound check is trivially satisfied, ri = p reads sizeof(struct ceph_mds_snap_realm) past the legitimate msg->front buffer, and ri->num_snaps / ri->num_prior_parent_snaps then drive further out-of-bounds reads of the encoded snap arrays.
The eleven msg_version >= 2 .. msg_version >= 12 decoder blocks above the op switch each catch this OOB through their ceph_decode_*_safe() / ceph_decode_need() helpers, but they sit behind a hdr.version-gated if, so a malicious or compromised MDS that sets msg->hdr.version = 1 reaches the IMPORT path with no version-gated decoder having validated snap_trace_len. The shape has been present since ceph_handle_caps() was introduced.
Validate snap_trace_len against the message front buffer before consuming it, using the canonical ceph_decode_need() / ceph_has_room() helper. The helper bounds the length with subtraction (n <= end - p, guarded by end >= p) rather than pointer addition, so it is wrap-safe for the attacker-controlled u32 length on 32-bit builds where p + snap_trace_len could overflow the address space. This matches the rest of the ceph decode path (e.g. the pool_ns_len check a few lines below), and the existing goto bad cleanup already covers this exit path.
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Analysis
by VulDB Data Team • 08/10/2026
The vulnerability described involves an out-of-bounds read in the Linux kernel's Ceph distributed file system implementation, specifically within the ceph_handle_caps() function. This flaw arises from improper validation of the snap_trace_len field received from network messages, creating a condition where attacker-controlled data can lead to memory access violations. The issue manifests when processing CAPS operations in the CEPH_CAP_OP_IMPORT case, where the length parameter is used directly without sufficient bounds checking against the actual message buffer boundaries.
The technical implementation of this vulnerability exploits a classic buffer overflow pattern through improper pointer arithmetic and length validation. The snaptrace_len value is extracted from the wire-format header without verification against the legitimate message buffer limits, allowing an attacker to specify an arbitrarily large value that when added to the snaptrace pointer results in a pointer that extends beyond the valid memory region. This creates a scenario where ceph_update_snap_trace() attempts to decode structured data from memory locations that may not contain the expected data format, leading to information disclosure and potential system instability.
The operational impact of this vulnerability spans multiple security domains including information disclosure and denial-of-service conditions. An attacker with access to communicate with a Ceph MDS server could craft malicious messages that trigger the out-of-bounds read, potentially exposing kernel memory contents or causing system crashes. The vulnerability affects systems using Ceph versions where the message version is set to 1, bypassing the normal validation mechanisms present in newer message formats. This represents a critical security concern for distributed storage environments relying on Ceph as their backend file system.
The root cause analysis reveals a fundamental flaw in the kernel's decoding logic that fails to implement proper bounds checking before processing attacker-controllable data lengths. The vulnerability aligns with CWE-129 Input Validation and CWE-787 Out-of-bounds Write patterns, though specifically manifests as an out-of-bounds read condition. The solution requires implementing proper validation using established kernel decoding helpers such as ceph_decode_need() and ceph_has_room(), which perform subtraction-based bounds checks rather than pointer addition to prevent integer overflow issues on 32-bit systems. This approach ensures that the length parameter cannot exceed available buffer space, preventing memory access violations.
The fix strategy addresses the core issue by validating snap_trace_len against the actual message front buffer boundaries before using it in any memory operations. This implementation follows established kernel security patterns and matches existing validation practices within the same codebase, such as the pool_ns_len check mentioned in the description. The approach uses wrap-safe arithmetic that prevents attackers from creating pointer overflows through malicious length values, specifically addressing concerns with 32-bit address space limitations where simple pointer addition could result in overflow conditions. This defensive programming technique ensures that memory operations remain within legitimate buffer boundaries regardless of input values.
The mitigation strategy leverages existing kernel security infrastructure and maintains consistency with established decoding patterns throughout the Ceph implementation. The solution integrates seamlessly with the current error handling mechanisms, utilizing the existing goto bad cleanup path for proper resource management and error recovery. This approach prevents both immediate exploitation opportunities and potential follow-on vulnerabilities that could arise from corrupted memory states. The fix addresses not only the immediate out-of-bounds read but also prevents related security issues that might stem from improper buffer management in similar decoding contexts within the same subsystem.
Security practitioners should prioritize patching affected Ceph installations to prevent exploitation of this vulnerability, particularly in environments where untrusted network access is possible. The vulnerability demonstrates the importance of validating all attacker-controllable inputs before using them in memory operations and highlights the need for consistent security practices throughout kernel subsystems. This case study reinforces standard security recommendations including input validation, bounds checking, and defensive programming techniques that protect against buffer overflow conditions in network protocols and data processing systems.