{"id":"CVE-2026-63887","state":"PUBLISHED","title":"scsi: target: iscsi: Bound iscsi_encode_text_output() appends to rsp_buf","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nscsi: target: iscsi: Bound iscsi_encode_text_output() appends to rsp_buf\n\niscsi_encode_text_output() concatenates \"key=value\\0\" records into\nlogin->rsp_buf, an 8192-byte kzalloc(MAX_KEY_VALUE_PAIRS) buffer\nallocated in iscsit_alloc_login_setup_buffer(). The three sprintf() call\nsites in this function (lines 1398, 1411, 1424 in v7.1-rc2) never check\nthe remaining buffer capacity:\n\n\t*length += sprintf(output_buf, \"%s=%s\", er->key, er->value);\n\t*length += 1;\n\toutput_buf = textbuf + *length;\n\nThe 8192-byte ceiling at iscsi_target_check_login_request() bounds the\n*input* Login PDU payload, but a single PDU can carry up to 2048 minimal\nfour-byte \"a=b\\0\" pairs, each unknown key expanding to a 16-byte\n\"a=NotUnderstood\\0\" output record via iscsi_add_notunderstood_response().\n2048 * 16 = 32 KiB of output into an 8 KiB buffer, producing a ~24 KiB\nheap overrun in the kmalloc-8k slab.\n\nThe fix introduces a static iscsi_encode_text_record() helper that uses\nsnprintf() with a per-call bounds check against the remaining buffer,\nand threads a u32 textbuf_size parameter through\niscsi_encode_text_output(). Both call sites in\niscsi_target_handle_csg_zero() (PHASE_SECURITY) and\niscsi_target_handle_csg_one() (PHASE_OPERATIONAL) pass\nMAX_KEY_VALUE_PAIRS. On overflow the encoder logs the condition, calls\niscsi_release_extra_responses() to drop queued records, and returns -1;\nboth caller sites now emit ISCSI_STATUS_CLS_INITIATOR_ERR /\nISCSI_LOGIN_STATUS_INIT_ERR via iscsit_tx_login_rsp() before returning,\nso the initiator sees an explicit failed-login response rather than a\nsilent connection drop. (Prior to this patch only the PHASE_OPERATIONAL\ncaller did that; the PHASE_SECURITY caller is converted to the same\nshape.)","publishedAt":"2026-07-19T14:55:00.114Z","updatedAt":"2026-10-19T20:17:54.668Z","severity":{"score":9.8,"label":"Critical","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"e48354ce078c079996f89d715dfa44814b4eba01","status":"affected","lessThan":"cb84e974fb172bc71386289f37b78ea679410b39","versionType":"git"},{"version":"e48354ce078c079996f89d715dfa44814b4eba01","status":"affected","lessThan":"b19382dfc6e7dee6d3859ba44b6ca29e97a51627","versionType":"git"},{"version":"e48354ce078c079996f89d715dfa44814b4eba01","status":"affected","lessThan":"efe633e600a0ac68357206fede21b1ac8178f3b8","versionType":"git"},{"version":"e48354ce078c079996f89d715dfa44814b4eba01","status":"affected","lessThan":"4e9f0c4a645c995bc75c06c7b3644254ffb4c76b","versionType":"git"},{"version":"e48354ce078c079996f89d715dfa44814b4eba01","status":"affected","lessThan":"30bf335e8fe170322080ee001f05ca29c50680b3","versionType":"git"},{"version":"e48354ce078c079996f89d715dfa44814b4eba01","status":"affected","lessThan":"594a40360012ce5f94c715d5e3b20fa3af7d525a","versionType":"git"},{"version":"e48354ce078c079996f89d715dfa44814b4eba01","status":"affected","lessThan":"26e4a304b7e6f1338c675d527608d32549c091db","versionType":"git"},{"version":"e48354ce078c079996f89d715dfa44814b4eba01","status":"affected","lessThan":"bf33e01f88388c43e285492a63e539df6ffed64c","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/target/iscsi/iscsi_target_nego.c","drivers/target/iscsi/iscsi_target_parameters.c","drivers/target/iscsi/iscsi_target_parameters.h"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"3.1","status":"affected"},{"version":"0","status":"unaffected","lessThan":"3.1","versionType":"semver"},{"version":"5.10.259","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.210","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.176","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.143","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.93","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.35","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.0.12","status":"unaffected","lessThanOrEqual":"7.0.*","versionType":"semver"},{"version":"7.1","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/target/iscsi/iscsi_target_nego.c","drivers/target/iscsi/iscsi_target_parameters.c","drivers/target/iscsi/iscsi_target_parameters.h"]}],"references":["https://git.kernel.org/stable/c/cb84e974fb172bc71386289f37b78ea679410b39","https://git.kernel.org/stable/c/b19382dfc6e7dee6d3859ba44b6ca29e97a51627","https://git.kernel.org/stable/c/efe633e600a0ac68357206fede21b1ac8178f3b8","https://git.kernel.org/stable/c/4e9f0c4a645c995bc75c06c7b3644254ffb4c76b","https://git.kernel.org/stable/c/30bf335e8fe170322080ee001f05ca29c50680b3","https://git.kernel.org/stable/c/594a40360012ce5f94c715d5e3b20fa3af7d525a","https://git.kernel.org/stable/c/26e4a304b7e6f1338c675d527608d32549c091db","https://git.kernel.org/stable/c/bf33e01f88388c43e285492a63e539df6ffed64c"],"weaknesses":["CWE-122"],"ingestedAt":"2026-10-29T20:12:41.951Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/63xxx/CVE-2026-63887.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-63887","state":"PUBLISHED","datePublished":"2026-07-19T14:55:00.114Z","dateUpdated":"2026-10-19T20:17:54.668Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-07-19T07:54:57.018Z"},"containers":{"cna":{"title":"scsi: target: iscsi: Bound iscsi_encode_text_output() appends to rsp_buf","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nscsi: target: iscsi: Bound iscsi_encode_text_output() appends to rsp_buf\n\niscsi_encode_text_output() concatenates \"key=value\\0\" records into\nlogin->rsp_buf, an 8192-byte kzalloc(MAX_KEY_VALUE_PAIRS) buffer\nallocated in iscsit_alloc_login_setup_buffer(). The three sprintf() call\nsites in this function (lines 1398, 1411, 1424 in v7.1-rc2) never check\nthe remaining buffer capacity:\n\n\t*length += sprintf(output_buf, \"%s=%s\", er->key, er->value);\n\t*length += 1;\n\toutput_buf = textbuf + *length;\n\nThe 8192-byte ceiling at iscsi_target_check_login_request() bounds the\n*input* Login PDU payload, but a single PDU can carry up to 2048 minimal\nfour-byte \"a=b\\0\" pairs, each unknown key expanding to a 16-byte\n\"a=NotUnderstood\\0\" output record via iscsi_add_notunderstood_response().\n2048 * 16 = 32 KiB of output into an 8 KiB buffer, producing a ~24 KiB\nheap overrun in the kmalloc-8k slab.\n\nThe fix introduces a static iscsi_encode_text_record() helper that uses\nsnprintf() with a per-call bounds check against the remaining buffer,\nand threads a u32 textbuf_size parameter through\niscsi_encode_text_output(). Both call sites in\niscsi_target_handle_csg_zero() (PHASE_SECURITY) and\niscsi_target_handle_csg_one() (PHASE_OPERATIONAL) pass\nMAX_KEY_VALUE_PAIRS. On overflow the encoder logs the condition, calls\niscsi_release_extra_responses() to drop queued records, and returns -1;\nboth caller sites now emit ISCSI_STATUS_CLS_INITIATOR_ERR /\nISCSI_LOGIN_STATUS_INIT_ERR via iscsit_tx_login_rsp() before returning,\nso the initiator sees an explicit failed-login response rather than a\nsilent connection drop. (Prior to this patch only the PHASE_OPERATIONAL\ncaller did that; the PHASE_SECURITY caller is converted to the same\nshape.)"}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"e48354ce078c079996f89d715dfa44814b4eba01","status":"affected","lessThan":"cb84e974fb172bc71386289f37b78ea679410b39","versionType":"git"},{"version":"e48354ce078c079996f89d715dfa44814b4eba01","status":"affected","lessThan":"b19382dfc6e7dee6d3859ba44b6ca29e97a51627","versionType":"git"},{"version":"e48354ce078c079996f89d715dfa44814b4eba01","status":"affected","lessThan":"efe633e600a0ac68357206fede21b1ac8178f3b8","versionType":"git"},{"version":"e48354ce078c079996f89d715dfa44814b4eba01","status":"affected","lessThan":"4e9f0c4a645c995bc75c06c7b3644254ffb4c76b","versionType":"git"},{"version":"e48354ce078c079996f89d715dfa44814b4eba01","status":"affected","lessThan":"30bf335e8fe170322080ee001f05ca29c50680b3","versionType":"git"},{"version":"e48354ce078c079996f89d715dfa44814b4eba01","status":"affected","lessThan":"594a40360012ce5f94c715d5e3b20fa3af7d525a","versionType":"git"},{"version":"e48354ce078c079996f89d715dfa44814b4eba01","status":"affected","lessThan":"26e4a304b7e6f1338c675d527608d32549c091db","versionType":"git"},{"version":"e48354ce078c079996f89d715dfa44814b4eba01","status":"affected","lessThan":"bf33e01f88388c43e285492a63e539df6ffed64c","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/target/iscsi/iscsi_target_nego.c","drivers/target/iscsi/iscsi_target_parameters.c","drivers/target/iscsi/iscsi_target_parameters.h"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"3.1","status":"affected"},{"version":"0","status":"unaffected","lessThan":"3.1","versionType":"semver"},{"version":"5.10.259","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.210","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.176","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.143","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.93","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.35","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.0.12","status":"unaffected","lessThanOrEqual":"7.0.*","versionType":"semver"},{"version":"7.1","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/target/iscsi/iscsi_target_nego.c","drivers/target/iscsi/iscsi_target_parameters.c","drivers/target/iscsi/iscsi_target_parameters.h"]}],"references":[{"url":"https://git.kernel.org/stable/c/cb84e974fb172bc71386289f37b78ea679410b39"},{"url":"https://git.kernel.org/stable/c/b19382dfc6e7dee6d3859ba44b6ca29e97a51627"},{"url":"https://git.kernel.org/stable/c/efe633e600a0ac68357206fede21b1ac8178f3b8"},{"url":"https://git.kernel.org/stable/c/4e9f0c4a645c995bc75c06c7b3644254ffb4c76b"},{"url":"https://git.kernel.org/stable/c/30bf335e8fe170322080ee001f05ca29c50680b3"},{"url":"https://git.kernel.org/stable/c/594a40360012ce5f94c715d5e3b20fa3af7d525a"},{"url":"https://git.kernel.org/stable/c/26e4a304b7e6f1338c675d527608d32549c091db"},{"url":"https://git.kernel.org/stable/c/bf33e01f88388c43e285492a63e539df6ffed64c"}],"metrics":[{"cvssV3_1":{"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"},"scenarios":[{"lang":"en","value":"AV:N - The Linux iSCSI target (LIO) is an in-kernel SCSI target that accepts remote TCP connections on the iSCSI portal (typically port 3260); crafted Login PDUs reach the vulnerable encoder via the normal network receive and login-negotiation path.\nAC:L - Once an iSCSI target portal is reachable, an attacker can reliably trigger the overflow by sending a single Login PDU packed with unknown key=value pairs; no races or victim-dependent timing are required.\nPR:N - The heap overflow occurs during login negotiation before iSCSI authentication completes; a discovery-session login requires only InitiatorName and SessionType with no credentials, initiator ACL, or local privileges.\nUI:N - Exploitation requires only network packets sent by the attacker; no action from a legitimate user or administrator is needed beyond the target already exposing its iSCSI portal.\nS:U - The corruption is confined to kernel heap memory in the iSCSI target/login context and does not cross a VM, container, or IOMMU security boundary by itself.\nC:H - A ~24 KiB out-of-bounds write into the kmalloc-8k slab can corrupt adjacent kernel objects and be leveraged for arbitrary memory disclosure, not merely a bounded leak.\nI:H - The unbounded sprintf heap overrun is a large out-of-bounds write that can corrupt adjacent heap metadata or objects to achieve arbitrary kernel memory modification and potential code execution.\nA:H - Corrupting kmalloc-8k heap objects during login response encoding can cause kernel oops, BUG, or panic, and the attack can be repeated against an exposed iSCSI target."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-08-05T12:36:56.451Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.1","versionEndExcluding":"5.10.259"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.1","versionEndExcluding":"5.15.210"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.1","versionEndExcluding":"6.1.176"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.1","versionEndExcluding":"6.6.143"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.1","versionEndExcluding":"6.12.93"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.1","versionEndExcluding":"6.18.35"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.1","versionEndExcluding":"7.0.12"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.1","versionEndExcluding":"7.1"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"id":"CVE-2026-63887","role":"CISA Coordinator","options":[{"Exploitation":"none"},{"Automatable":"yes"},{"Technical Impact":"total"}],"version":"2.0.3","timestamp":"2026-10-16T15:32:57.099055Z"}}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-122","lang":"en","type":"CWE","description":"CWE-122 Heap-based Buffer Overflow"}]}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-10-19T20:17:54.668Z"}}]}}}