CVE-2026-52955

In the Linux kernel, the following vulnerability has been resolved:

libceph: Fix potential out-of-bounds access in crush_decode()

A message of type CEPH_MSG_OSD_MAP containing a crush map with at least one bucket has two fields holding the bucket algorithm. If the values in these two fields differ, an out-of-bounds access can occur. This is the case because the first algorithm field (alg) is used to allocate the correct amount of memory for a bucket of this type, while the second algorithm field inside the bucket (b->alg) is used in the subsequent processing.

This patch fixes the issue by adding a check that compares alg and b->alg and aborts the processing in case they differ. Furthermore, b->alg is set to 0 in this case, because the destruction of the crush map also uses this field to determine the bucket type, which can again result in an out-of-bounds access when trying to free the memory pointed to by the fields of the bucket. To correctly free the memory allocated for the bucket in such a case, the corresponding call to kfree is moved from the algorithm-specific crush_destroy_bucket functions to the generic crush_destroy_bucket().

Weakness

The product reads data past the end, or before the beginning, of the intended buffer.

Affected Software

Potential Mitigations

• Assume all input is malicious. Use an “accept known good” input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
• When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, “boat” may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as “red” or “blue.”
• Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code’s environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
• To reduce the likelihood of introducing an out-of-bounds read, ensure that you validate and ensure correct calculations for any length argument, buffer size calculation, or offset. Be especially careful of relying on a sentinel (i.e. special character such as NUL) in untrusted inputs.

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/540.html

References

• https://git.kernel.org/stable/c/0f3604cbe4df14c5e58288ac9f57511e726a222d
• https://git.kernel.org/stable/c/3f42508191e129ee6b5ea96578d5cab14f2a013a
• https://git.kernel.org/stable/c/4c79fc2d598694bda845b46229c9d48b65042970
• https://git.kernel.org/stable/c/6e70ef53e818c53eab28d7b0026b7fd03dddaba5
• https://git.kernel.org/stable/c/cceb10023e76bc89f3fe9238ebd0ccab0fc7c7c5
• https://git.kernel.org/stable/c/ea0d42137f0c06da71e37ffc647aab4c5309599a
• https://git.kernel.org/stable/c/ebe76d58a48a48031b98543d86c4cd30a825b622
• https://git.kernel.org/stable/c/fb176a99e4c1a5a8448a83d83d3606203ba81faa
• https://access.redhat.com/security/cve/CVE-2026-52955
• https://bugzilla.redhat.com/show_bug.cgi?id=2492328
• https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-52955.json