CVE-2026-63886Critical· 9.8▾ MidnightIn 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-…
▾ Midnight zone — Critical, or high with PoC / in-the-wild
impact 53.9 · likelihood 0.1 · exploitation 0
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Stakeholder-Specific Vulnerability Categorization from CISA's ADP record at CVE.org: whether exploitation is observed, whether an attack can be automated, and how much of the system is at stake. The CVSS score shown above comes from the assigning CNA record, not NVD.
Exploit-prediction probability, daily snapshots since Oct 16.
Disclosure to exploitation, from the record and what we observed since indexing it.
Disclosed via CVEORG
0.7%
Last analysed / modified upstream
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: strip trailing base64 padding characters, then reject any input whose data length exceeds DIV_ROUND_UP(digest_size * 4, 3) before calling the decoder.
Stripping trailing '=' before the comparison handles both padded and unpadded encodings. chap_base64_decode() already returns early on '=', so the full original string is still passed to the decoder unchanged.
The mutual CHAP path decodes CHAP_C into initiatorchg_binhex, which is kzalloc(CHAP_CHALLENGE_STR_LEN). extract_param() caps initiatorchg at CHAP_CHALLENGE_STR_LEN characters, so at most CHAP_CHALLENGE_STR_LEN-1 base64 characters reach the decoder. The maximum decoded size, DIV_ROUND_UP((CHAP_CHALLENGE_STR_LEN-1) * 3, 4), is less than CHAP_CHALLENGE_STR_LEN, so no overflow is possible there. A comment is added at the call site to document this.
Linux >= 1e5733883421495908f3b90d9d807663038b4136 < 82454e6f21e56ea9a0a9de7d0ff7e1dfb83e34d6Linux >= 1e5733883421495908f3b90d9d807663038b4136 < edd06675a02376ea8347dba7c29ad982ba5b36eeLinux >= 1e5733883421495908f3b90d9d807663038b4136 < bf154c657828ed05399bca5d98cf1611bb048b12Linux >= 1e5733883421495908f3b90d9d807663038b4136 < 4a3a19c98a8207ad08bec554703d90f2c34a8cc6Linux >= 1e5733883421495908f3b90d9d807663038b4136 < c04e85799356120209b351a148ac2db888d5ffd9Linux >= 1e5733883421495908f3b90d9d807663038b4136 < 85db7391310b1304d2dc8ae3b0b12105a9567147Linux 6.0Refer to the linked advisories for vendor-supplied fixes and affected version ranges.
Connected by shared product, vendor, weakness, or advisory.
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