{"cve":"CVE-2026-63888","nvd":{"published":"2026-07-19T16:17:05.997","modified":"2026-10-19T21:17:09.710","status":"Undergoing Analysis","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nscsi: target: iscsi: Fix CRC overread and double-free in iscsit_handle_text_cmd()\n\nTwo latent bugs in the Text-phase handler, both present since the\noriginal LIO integration in commit e48354ce078c (\"iscsi-target: Add\niSCSI fabric support for target v4.1\"):\n\n1) DataDigest CRC buffer overread (4 bytes past text_in).\n\n   text_in is kzalloc()'d at ALIGN(payload_length, 4).  rx_size is then\n   incremented by ISCSI_CRC_LEN to make room for the received DataDigest\n   in the iovec, but the same (now-bumped) rx_size is passed as the\n   buffer length to iscsit_crc_buf():\n\n       if (conn->conn_ops->DataDigest) {\n               ...\n               rx_size += ISCSI_CRC_LEN;\n       }\n       ...\n       if (conn->conn_ops->DataDigest) {\n               data_crc = iscsit_crc_buf(text_in, rx_size, 0, NULL);\n\n   iscsit_crc_buf() walks rx_size bytes of text_in with crc32c(), so\n   when DataDigest is negotiated it reads 4 bytes past the end of the\n   text_in allocation.  KASAN reproduces this directly on the unpatched\n   mainline tree as slab-out-of-bounds in crc32c() called from the Text\n   PDU path.  The OOB bytes feed crc32c() and are then compared against\n   the initiator-supplied checksum, so the value does not flow back to\n   the attacker, but the kernel does read past the buffer on every Text\n   PDU with DataDigest=CRC32C.\n\n   Fix by passing the actual padded payload length\n   (ALIGN(payload_length, 4)) that was used for the kzalloc().\n\n2) Stale cmd->text_in_ptr re-free (double-free) on ERL>0 bad DataDigest\n   drop.\n\n   On DataDigest mismatch with ErrorRecoveryLevel > 0 the handler\n   silently drops the PDU and lets the initiator plug the CmdSN gap:\n\n               kfree(text_in);\n               return 0;\n\n   cmd->text_in_ptr still points at the freed buffer.  The next Text\n   Request on the same ITT re-enters iscsit_setup_text_cmd(), which\n   unconditionally does\n\n       kfree(cmd->text_in_ptr);\n       cmd->text_in_ptr = NULL;\n\n   freeing the same pointer a second time.  Session teardown via\n   iscsit_release_cmd() has the same shape and hits the same double-free\n   if the connection is dropped before a second Text Request arrives.\n\n   On an unmodified mainline tree the bug-1 CRC overread fires first on\n   the initial valid Text Request and perturbs the subsequent state, so\n   #4 was isolated by building a kernel with only the bug-1 hunk of this\n   patch applied plus temporary printk() observability around the three\n   relevant kfree() sites.  The observability prints are not part of\n   this patch.  On that build, a three-PDU Text Request sequence after\n   login produces two back-to-back splats:\n\n       BUG: KASAN: double-free in iscsit_setup_text_cmd+0x??\n       BUG: KASAN: double-free in iscsit_release_cmd+0x??\n\n   showing the same pointer freed in the ERL>0 drop path and again in\n   iscsit_setup_text_cmd() (next Text Request on the same ITT) and once\n   more in iscsit_release_cmd() (session teardown).  On distro kernels\n   with CONFIG_SLAB_FREELIST_HARDENED=y (default) the double-free\n   becomes a remote kernel BUG(); on non-hardened kernels it corrupts\n   the slab freelist.\n\n   Fix by clearing cmd->text_in_ptr after the kfree() in the ERL>0 drop\n   path.  With both hunks applied #4 is directly observable on the stock\n   tree without observability printks; fixing bug-1 alone would mask #4\n   less, not more, so the hunks are submitted together.\n\nBoth fixes are one-liners.  The Text PDU state machine is unchanged and\nthe wire protocol is unaffected.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","score":9.8},"cwes":["CWE-415"],"references":["https://git.kernel.org/stable/c/5118ea225fe63b44207ba88047e4866e1ea43812","https://git.kernel.org/stable/c/6e22a1cdcc8277af4acc43710577157b77a02c5d","https://git.kernel.org/stable/c/778c2ab142c625a8a8afa570e0f9b7873f445d99","https://git.kernel.org/stable/c/89c81d1228c00fa6dd91de6c1c5aa1ef8a7875e3","https://git.kernel.org/stable/c/badf178b76b0690851df00f4ca9cf2eb8eb0f963"],"products":[],"source":"nvd","synced_at":"2026-10-21T03:43:09.190223697+00:00"},"epss":{"cve":"CVE-2026-63888","score":0.00778,"percentile":0.55574,"date":"2026-10-25"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}