{"id":"CVE-2026-89778","summary":"isofs: fix out-of-bounds page array access on empty zisofs block","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nisofs: fix out-of-bounds page array access on empty zisofs block\n\nzisofs_uncompress_block()'s empty-block fast path returns\npcount \u003c\u003c PAGE_SHIFT, ignoring the incoming poffset, unlike the\ndecompression path which returns bytes produced relative to poffset.\nzisofs_fill_pages() uses that return to advance its page cursor, so when\nthe zisofs block size is below PAGE_SIZE and a sub-page block leaves\npoffset partway into a page, a following empty block over-counts and\nadvances pages[] one element past its end, after which\n\"if (poffset && *pages)\" reads pages[1] out of bounds.  rock.c only\nrejects a block-size shift \u003e 17, so a crafted \"ZF\" Rock Ridge record can\nset it below PAGE_SHIFT; the bug is reached by an ordinary read() of a\ncompressed file on such a mounted ISO9660 image.\n\nReturn the byte count relative to poffset and zero only\n[poffset, PAGE_SIZE) of the first page, matching the decompression path.\nThe page-aligned case (poffset == 0) is unaffected.\n\n  BUG: KASAN: slab-out-of-bounds in zisofs_read_folio (fs/isofs/compress.c:290)\n  Read of size 8 at addr ffff88800f5eac48 by task exploit/142\n   zisofs_read_folio (fs/isofs/compress.c:290)\n   read_pages (mm/readahead.c:184)\n   ...\n   filemap_read (mm/filemap.c:2814)\n   vfs_read (fs/read_write.c:574)\n   __x64_sys_pread64 (fs/read_write.c:769)\n   do_syscall_64 (arch/x86/entry/syscall_64.c:94)\n   entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121)\n  The buggy address is located 0 bytes to the right of the\n  allocated 8-byte region in the kmalloc-8 cache","modified":"2026-09-18T03:48:32.709587150Z","published":"2026-09-16T08:48:18.407Z","database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/89xxx/CVE-2026-89778.json"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/68d4d3e78150c7ed7d1195af63ad1e6ace30c661"},{"type":"WEB","url":"https://git.kernel.org/stable/c/85904076cece72ee3194646ad7ac8e6659d999aa"},{"type":"WEB","url":"https://git.kernel.org/stable/c/8b994ac5778a725982fd6a8a3afcaa068d4a93e3"},{"type":"WEB","url":"https://git.kernel.org/stable/c/9c6eace8d07e90f038c89eb3b756d65a7e259d48"},{"type":"WEB","url":"https://git.kernel.org/stable/c/ad3249cdf9d4ba34bb8b1ff3956a4020fdfb5b0a"},{"type":"WEB","url":"https://git.kernel.org/stable/c/cd616aa0449a772a6956abf03358f0ff31720580"},{"type":"WEB","url":"https://git.kernel.org/stable/c/f03425dcbe04aec3c27b9917e97d7d23a2908dda"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/89xxx/CVE-2026-89778.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-89778"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"59bc055211b8d266ab6089158058bf8268e02006"},{"fixed":"8b994ac5778a725982fd6a8a3afcaa068d4a93e3"},{"fixed":"ad3249cdf9d4ba34bb8b1ff3956a4020fdfb5b0a"},{"fixed":"85904076cece72ee3194646ad7ac8e6659d999aa"},{"fixed":"f03425dcbe04aec3c27b9917e97d7d23a2908dda"},{"fixed":"cd616aa0449a772a6956abf03358f0ff31720580"},{"fixed":"9c6eace8d07e90f038c89eb3b756d65a7e259d48"},{"fixed":"68d4d3e78150c7ed7d1195af63ad1e6ace30c661"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-89778.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"2.6.33"},{"fixed":"5.15.221"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.16.0"},{"fixed":"6.1.188"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.2.0"},{"fixed":"6.6.157"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.7.0"},{"fixed":"6.12.110"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.18.52"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"7.2.6"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-89778.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"}]}