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

Type: advisorySource: Official CVE List1 source record

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_C

Announced Source revision 1
Original source ↗

CVE-2026-63886

Primary source · Revision 1

Imported from structured advisory data. Source references identify upstream records or fields; verify affected versions and your deployed configuration.

Security context

Source reference: cve:CVE-2026-63886

Linux

Source reference: /containers/cna/affected/0/product

Affected versions
Not stated in this record
Fixed versions
Not stated in this record
Prerequisites
Not stated in this record

Linux

Source reference: /containers/cna/affected/1/product

Affected versions
Not stated in this record
Fixed versions
Not stated in this record
Prerequisites
Not stated in this record

Structured affected-version data

Original package identities and version rules from this source.

[
  {
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "vendor": "Linux",
    "product": "Linux",
    "versions": [
      {
        "status": "affected",
        "version": "1e5733883421495908f3b90d9d807663038b4136",
        "lessThan": "82454e6f21e56ea9a0a9de7d0ff7e1dfb83e34d6",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "1e5733883421495908f3b90d9d807663038b4136",
        "lessThan": "edd06675a02376ea8347dba7c29ad982ba5b36ee",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "1e5733883421495908f3b90d9d807663038b4136",
        "lessThan": "bf154c657828ed05399bca5d98cf1611bb048b12",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "1e5733883421495908f3b90d9d807663038b4136",
        "lessThan": "4a3a19c98a8207ad08bec554703d90f2c34a8cc6",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "1e5733883421495908f3b90d9d807663038b4136",
        "lessThan": "c04e85799356120209b351a148ac2db888d5ffd9",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "1e5733883421495908f3b90d9d807663038b4136",
        "lessThan": "85db7391310b1304d2dc8ae3b0b12105a9567147",
        "versionType": "git"
      }
    ],
    "programFiles": [
      "drivers/target/iscsi/iscsi_target_auth.c"
    ],
    "defaultStatus": "unaffected"
  },
  {
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "vendor": "Linux",
    "product": "Linux",
    "versions": [
      {
        "status": "affected",
        "version": "6.0"
      },
      {
        "status": "unaffected",
        "version": "0",
        "lessThan": "6.0",
        "versionType": "semver"
      },
      {
        "status": "unaffected",
        "version": "6.1.176",
        "versionType": "semver",
        "lessThanOrEqual": "6.1.*"
      },
      {
        "status": "unaffected",
        "version": "6.6.143",
        "versionType": "semver",
        "lessThanOrEqual": "6.6.*"
      },
      {
        "status": "unaffected",
        "version": "6.12.93",
        "versionType": "semver",
        "lessThanOrEqual": "6.12.*"
      },
      {
        "status": "unaffected",
        "version": "6.18.35",
        "versionType": "semver",
        "lessThanOrEqual": "6.18.*"
      },
      {
        "status": "unaffected",
        "version": "7.0.12",
        "versionType": "semver",
        "lessThanOrEqual": "7.0.*"
      },
      {
        "status": "unaffected",
        "version": "7.1",
        "versionType": "original_commit_for_fix",
        "lessThanOrEqual": "*"
      }
    ],
    "programFiles": [
      "drivers/target/iscsi/iscsi_target_auth.c"
    ],
    "defaultStatus": "affected"
  }
]
Related CVEs
CVE-2026-63886

Source reference: /cveMetadata/cveId

Publisher severity

critical

Source reference: /containers/cna/metrics

Event
#40882 · Revision 1
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Publisher date
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