{"api_version":"1","generated_at":"2026-07-20T18:16:20+00:00","cve":"CVE-2026-63886","urls":{"html":"https://cve.report/CVE-2026-63886","api":"https://cve.report/api/cve/CVE-2026-63886.json","docs":"https://cve.report/api","cve_org":"https://www.cve.org/CVERecord?id=CVE-2026-63886","nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-63886"},"summary":{"title":"scsi: target: iscsi: Validate CHAP_R length before base64 decode","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nscsi: target: iscsi: Validate CHAP_R length before base64 decode\n\nchap_server_compute_hash() allocates client_digest as\nkzalloc(chap->digest_size) and then, for BASE64-encoded responses,\npasses chap_r directly to chap_base64_decode() without checking whether\nthe input length could produce more than digest_size bytes of output.\n\nchap_base64_decode() writes to the destination unconditionally as long\nas there is input to consume. With MAX_RESPONSE_LENGTH set to 128 and\nthe \"0b\" prefix stripped by extract_param(), up to 127 base64 characters\ncan reach the decoder. 127 characters decode to 95 bytes. For SHA-256\n(digest_size=32) this overflows client_digest by 63 bytes; for MD5\n(digest_size=16) the overflow is 79 bytes.\n\nThe length check at line 344 fires after the write has already happened.\n\nThe HEX branch in the same switch statement already validates the length\nup front. Apply the same approach to the BASE64 branch: strip trailing\nbase64 padding characters, then reject any input whose data length\nexceeds DIV_ROUND_UP(digest_size * 4, 3) before calling the decoder.\n\nStripping trailing '=' before the comparison handles both padded and\nunpadded encodings. chap_base64_decode() already returns early on '=',\nso the full original string is still passed to the decoder unchanged.\n\nThe mutual CHAP path decodes CHAP_C into initiatorchg_binhex, which is\nkzalloc(CHAP_CHALLENGE_STR_LEN). extract_param() caps initiatorchg at\nCHAP_CHALLENGE_STR_LEN characters, so at most CHAP_CHALLENGE_STR_LEN-1\nbase64 characters reach the decoder. The maximum decoded size,\nDIV_ROUND_UP((CHAP_CHALLENGE_STR_LEN-1) * 3, 4), is less than\nCHAP_CHALLENGE_STR_LEN, so no overflow is possible there. A comment is\nadded at the call site to document this.","state":"PUBLISHED","assigner":"Linux","published_at":"2026-07-19 16:17:05","updated_at":"2026-07-20 15:16:53"},"problem_types":[],"metrics":[{"version":"3.1","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","type":"Secondary","score":"9.8","severity":"CRITICAL","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","data":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","baseScore":9.8,"baseSeverity":"CRITICAL","attackVector":"NETWORK","attackComplexity":"LOW","privilegesRequired":"NONE","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"HIGH","integrityImpact":"HIGH","availabilityImpact":"HIGH"}},{"version":"3.1","source":"CNA","type":"DECLARED","score":"9.8","severity":"CRITICAL","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","data":{"baseScore":9.8,"baseSeverity":"CRITICAL","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","version":"3.1"}}],"references":[{"url":"https://git.kernel.org/stable/c/bf154c657828ed05399bca5d98cf1611bb048b12","name":"https://git.kernel.org/stable/c/bf154c657828ed05399bca5d98cf1611bb048b12","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/85db7391310b1304d2dc8ae3b0b12105a9567147","name":"https://git.kernel.org/stable/c/85db7391310b1304d2dc8ae3b0b12105a9567147","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/82454e6f21e56ea9a0a9de7d0ff7e1dfb83e34d6","name":"https://git.kernel.org/stable/c/82454e6f21e56ea9a0a9de7d0ff7e1dfb83e34d6","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/4a3a19c98a8207ad08bec554703d90f2c34a8cc6","name":"https://git.kernel.org/stable/c/4a3a19c98a8207ad08bec554703d90f2c34a8cc6","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/edd06675a02376ea8347dba7c29ad982ba5b36ee","name":"https://git.kernel.org/stable/c/edd06675a02376ea8347dba7c29ad982ba5b36ee","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/c04e85799356120209b351a148ac2db888d5ffd9","name":"https://git.kernel.org/stable/c/c04e85799356120209b351a148ac2db888d5ffd9","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-63886","name":"CVE Program record","refsource":"CVE.ORG","tags":["canonical"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-63886","name":"NVD vulnerability detail","refsource":"NVD","tags":["canonical","analysis"]}],"affected":[{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 1e5733883421495908f3b90d9d807663038b4136 82454e6f21e56ea9a0a9de7d0ff7e1dfb83e34d6 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 1e5733883421495908f3b90d9d807663038b4136 edd06675a02376ea8347dba7c29ad982ba5b36ee git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 1e5733883421495908f3b90d9d807663038b4136 bf154c657828ed05399bca5d98cf1611bb048b12 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 1e5733883421495908f3b90d9d807663038b4136 4a3a19c98a8207ad08bec554703d90f2c34a8cc6 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 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the Linux kernel, the following vulnerability has been resolved:\n\nscsi: target: iscsi: Validate CHAP_R length before base64 decode\n\nchap_server_compute_hash() allocates client_digest as\nkzalloc(chap->digest_size) and then, for BASE64-encoded responses,\npasses chap_r directly to chap_base64_decode() without checking whether\nthe input length could produce more than digest_size bytes of output.\n\nchap_base64_decode() writes to the destination unconditionally as long\nas there is input to consume. With MAX_RESPONSE_LENGTH set to 128 and\nthe \"0b\" prefix stripped by extract_param(), up to 127 base64 characters\ncan reach the decoder. 127 characters decode to 95 bytes. For SHA-256\n(digest_size=32) this overflows client_digest by 63 bytes; for MD5\n(digest_size=16) the overflow is 79 bytes.\n\nThe length check at line 344 fires after the write has already happened.\n\nThe HEX branch in the same switch statement already validates the length\nup front. Apply the same approach to the BASE64 branch: strip trailing\nbase64 padding characters, then reject any input whose data length\nexceeds DIV_ROUND_UP(digest_size * 4, 3) before calling the decoder.\n\nStripping trailing '=' before the comparison handles both padded and\nunpadded encodings. chap_base64_decode() already returns early on '=',\nso the full original string is still passed to the decoder unchanged.\n\nThe mutual CHAP path decodes CHAP_C into initiatorchg_binhex, which is\nkzalloc(CHAP_CHALLENGE_STR_LEN). extract_param() caps initiatorchg at\nCHAP_CHALLENGE_STR_LEN characters, so at most CHAP_CHALLENGE_STR_LEN-1\nbase64 characters reach the decoder. The maximum decoded size,\nDIV_ROUND_UP((CHAP_CHALLENGE_STR_LEN-1) * 3, 4), is less than\nCHAP_CHALLENGE_STR_LEN, so no overflow is possible there. A comment is\nadded at the call site to document this."}],"metrics":[{"cvssV3_1":{"baseScore":9.8,"baseSeverity":"CRITICAL","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","version":"3.1"}}],"providerMetadata":{"dateUpdated":"2026-07-20T13:41:12.282Z","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux"},"references":[{"url":"https://git.kernel.org/stable/c/82454e6f21e56ea9a0a9de7d0ff7e1dfb83e34d6"},{"url":"https://git.kernel.org/stable/c/edd06675a02376ea8347dba7c29ad982ba5b36ee"},{"url":"https://git.kernel.org/stable/c/bf154c657828ed05399bca5d98cf1611bb048b12"},{"url":"https://git.kernel.org/stable/c/4a3a19c98a8207ad08bec554703d90f2c34a8cc6"},{"url":"https://git.kernel.org/stable/c/c04e85799356120209b351a148ac2db888d5ffd9"},{"url":"https://git.kernel.org/stable/c/85db7391310b1304d2dc8ae3b0b12105a9567147"}],"title":"scsi: target: iscsi: Validate CHAP_R length before base64 decode","x_generator":{"engine":"bippy-1.2.0"}}},"cveMetadata":{"assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","assignerShortName":"Linux","cveId":"CVE-2026-63886","datePublished":"2026-07-19T14:54:59.395Z","dateReserved":"2026-07-19T07:54:57.018Z","dateUpdated":"2026-07-20T13:41:12.282Z","state":"PUBLISHED"},"dataType":"CVE_RECORD","dataVersion":"5.2"},"nvd":{"publishedDate":"2026-07-19 16:17:05","lastModifiedDate":"2026-07-20 15:16:53","problem_types":[],"metrics":{"cvssMetricV31":[{"source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","type":"Secondary","cvssData":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","baseScore":9.8,"baseSeverity":"CRITICAL","attackVector":"NETWORK","attackComplexity":"LOW","privilegesRequired":"NONE","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"HIGH","integrityImpact":"HIGH","availabilityImpact":"HIGH"},"exploitabilityScore":3.9,"impactScore":5.9}]},"configurations":[]},"legacy_mitre":{"record":{"CveYear":"2026","CveId":"63886","Ordinal":"1","Title":"scsi: target: iscsi: Validate CHAP_R length before base64 decode","CVE":"CVE-2026-63886","Year":"2026"},"notes":[{"CveYear":"2026","CveId":"63886","Ordinal":"1","NoteData":"In the Linux kernel, the following vulnerability has been resolved:\n\nscsi: target: iscsi: Validate CHAP_R length before base64 decode\n\nchap_server_compute_hash() allocates client_digest as\nkzalloc(chap->digest_size) and then, for BASE64-encoded responses,\npasses chap_r directly to chap_base64_decode() without checking whether\nthe input length could produce more than digest_size bytes of output.\n\nchap_base64_decode() writes to the destination unconditionally as long\nas there is input to consume. With MAX_RESPONSE_LENGTH set to 128 and\nthe \"0b\" prefix stripped by extract_param(), up to 127 base64 characters\ncan reach the decoder. 127 characters decode to 95 bytes. For SHA-256\n(digest_size=32) this overflows client_digest by 63 bytes; for MD5\n(digest_size=16) the overflow is 79 bytes.\n\nThe length check at line 344 fires after the write has already happened.\n\nThe HEX branch in the same switch statement already validates the length\nup front. Apply the same approach to the BASE64 branch: strip trailing\nbase64 padding characters, then reject any input whose data length\nexceeds DIV_ROUND_UP(digest_size * 4, 3) before calling the decoder.\n\nStripping trailing '=' before the comparison handles both padded and\nunpadded encodings. chap_base64_decode() already returns early on '=',\nso the full original string is still passed to the decoder unchanged.\n\nThe mutual CHAP path decodes CHAP_C into initiatorchg_binhex, which is\nkzalloc(CHAP_CHALLENGE_STR_LEN). extract_param() caps initiatorchg at\nCHAP_CHALLENGE_STR_LEN characters, so at most CHAP_CHALLENGE_STR_LEN-1\nbase64 characters reach the decoder. The maximum decoded size,\nDIV_ROUND_UP((CHAP_CHALLENGE_STR_LEN-1) * 3, 4), is less than\nCHAP_CHALLENGE_STR_LEN, so no overflow is possible there. A comment is\nadded at the call site to document this.","Type":"Description","Title":"scsi: target: iscsi: Validate CHAP_R length before base64 decode"}]}}}