CVE-2026-63886

Technical Description

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

scsi: target: iscsi: Validate CHAP_R length before base64 decode

chap_server_compute_hash() allocates client_digest as

kzalloc(chap->digest_size) and then, for BASE64-encoded responses,

passes chap_r directly to chap_base64_decode() without checking whether

the input length could produce more than digest_size bytes of output.

chap_base64_decode() writes to the destination unconditionally as long

as there is input to consume. With MAX_RESPONSE_LENGTH set to 128 and

the "0b" prefix stripped by extract_param(), up to 127 base64 characters

can reach the decoder. 127 characters decode to 95 bytes. For SHA-256

(digest_size=32) this overflows client_digest by 63 bytes; for MD5

(digest_size=16) the overflow is 79 bytes.

The length check at line 344 fires after the write has already happened.

The HEX branch in the same switch statement already validates the length

up front. Apply the same approach to the BASE64 branch: str

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References