{"id":"CVE-2026-98983","state":"PUBLISHED","title":"unshare: don't drop active namespace references that were never taken","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nunshare: don't drop active namespace references that were never taken\n\nActive references on the namespaces of an nsproxy are taken when the\nnsproxy is installed into a task in switch_task_namespaces() and\ncopy_namespaces() and dropped again by put_nsproxy() through\ndeactivate_nsproxy().\n\nBut ksys_unshare() calls put_nsproxy() on an nsproxy that was never\ninstalled when set_cred_ucounts() fails. The new namespaces of that\nnsproxy go from zero to minus one and the namespaces shared with the\ncaller lose a reference that belongs to the nsproxy the caller keeps\nusing:\n\n  WARNING: kernel/nscommon.c:171 at __ns_ref_active_put+0x1cd/0x230\n   nsproxy_ns_active_put\n   deactivate_nsproxy\n   ksys_unshare\n\nAfterwards the namespaces the caller lives in aren't listed by listns()\nanymore. set_cred_ucounts() only fails when alloc_ucounts() can't\nallocate and it only allocates when the real uid of the caller differs\nfrom its effective uid.\n\nCommit cefd55bd2159 (\"nsproxy: fix free_nsproxy() and simplify\ncreate_new_namespaces()\") separated the two cases on purpose.\nnsproxy_free() frees an nsproxy that was prepared but never installed\nand that's what a failed setns() uses in put_nsset(). Export it and use\nit for a failed unshare() as well.","publishedAt":"2026-10-23T12:20:00.918Z","updatedAt":"2026-10-23T12:20:00.918Z","severity":null,"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"a98621a0f187a934c115dcfe79a49520ae892111","status":"affected","lessThan":"56fe03a0c05dba4c5f6a23c391f96de1614a098c","versionType":"git"},{"version":"a98621a0f187a934c115dcfe79a49520ae892111","status":"affected","lessThan":"0b6f31a3c0b16066f812e94b52a704174a6f23cd","versionType":"git"},{"version":"27ae6b17c9ba7ff353ab0906297f08aa845782b4","status":"affected","versionType":"git"},{"version":"297261b343371c4f0b31055d53d285138ec21565","status":"affected","versionType":"git"},{"version":"813a47b0309097da71781ee4ac11922e39b67d55","status":"affected","versionType":"git"},{"version":"6e608e3e5ce12ce7fd21e46212eccca37f917d0e","status":"affected","versionType":"git"},{"version":"a261fccdb4ac58ec5ba6aa1d92a6cc418fff301f","status":"affected","versionType":"git"},{"version":"665dc1ed16357988d439fc5bbc860ee36f540d81","status":"affected","versionType":"git"},{"version":"5.15.209","status":"affected","lessThan":"5.16","versionType":"semver"},{"version":"6.1.175","status":"affected","lessThan":"6.2","versionType":"semver"},{"version":"6.6.141","status":"affected","lessThan":"6.7","versionType":"semver"},{"version":"6.12.91","status":"affected","lessThan":"6.13","versionType":"semver"},{"version":"6.18.33","status":"affected","lessThan":"6.19","versionType":"semver"},{"version":"7.0.10","status":"affected","lessThan":"7.1","versionType":"semver"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["include/linux/nsproxy.h","kernel/fork.c","kernel/nsproxy.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"7.1","status":"affected"},{"version":"0","status":"unaffected","lessThan":"7.1","versionType":"semver"},{"version":"7.2.11","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["include/linux/nsproxy.h","kernel/fork.c","kernel/nsproxy.c"]}],"references":["https://git.kernel.org/stable/c/56fe03a0c05dba4c5f6a23c391f96de1614a098c","https://git.kernel.org/stable/c/0b6f31a3c0b16066f812e94b52a704174a6f23cd"],"weaknesses":[],"ingestedAt":"2026-10-29T20:13:43.249Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/98xxx/CVE-2026-98983.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-98983","state":"PUBLISHED","datePublished":"2026-10-23T12:20:00.918Z","dateUpdated":"2026-10-23T12:20:00.918Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-09-25T10:25:14.384Z"},"containers":{"cna":{"title":"unshare: don't drop active namespace references that were never taken","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nunshare: don't drop active namespace references that were never taken\n\nActive references on the namespaces of an nsproxy are taken when the\nnsproxy is installed into a task in switch_task_namespaces() and\ncopy_namespaces() and dropped again by put_nsproxy() through\ndeactivate_nsproxy().\n\nBut ksys_unshare() calls put_nsproxy() on an nsproxy that was never\ninstalled when set_cred_ucounts() fails. The new namespaces of that\nnsproxy go from zero to minus one and the namespaces shared with the\ncaller lose a reference that belongs to the nsproxy the caller keeps\nusing:\n\n  WARNING: kernel/nscommon.c:171 at __ns_ref_active_put+0x1cd/0x230\n   nsproxy_ns_active_put\n   deactivate_nsproxy\n   ksys_unshare\n\nAfterwards the namespaces the caller lives in aren't listed by listns()\nanymore. set_cred_ucounts() only fails when alloc_ucounts() can't\nallocate and it only allocates when the real uid of the caller differs\nfrom its effective uid.\n\nCommit cefd55bd2159 (\"nsproxy: fix free_nsproxy() and simplify\ncreate_new_namespaces()\") separated the two cases on purpose.\nnsproxy_free() frees an nsproxy that was prepared but never installed\nand that's what a failed setns() uses in put_nsset(). Export it and use\nit for a failed unshare() as well."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"a98621a0f187a934c115dcfe79a49520ae892111","status":"affected","lessThan":"56fe03a0c05dba4c5f6a23c391f96de1614a098c","versionType":"git"},{"version":"a98621a0f187a934c115dcfe79a49520ae892111","status":"affected","lessThan":"0b6f31a3c0b16066f812e94b52a704174a6f23cd","versionType":"git"},{"version":"27ae6b17c9ba7ff353ab0906297f08aa845782b4","status":"affected","versionType":"git"},{"version":"297261b343371c4f0b31055d53d285138ec21565","status":"affected","versionType":"git"},{"version":"813a47b0309097da71781ee4ac11922e39b67d55","status":"affected","versionType":"git"},{"version":"6e608e3e5ce12ce7fd21e46212eccca37f917d0e","status":"affected","versionType":"git"},{"version":"a261fccdb4ac58ec5ba6aa1d92a6cc418fff301f","status":"affected","versionType":"git"},{"version":"665dc1ed16357988d439fc5bbc860ee36f540d81","status":"affected","versionType":"git"},{"version":"5.15.209","status":"affected","lessThan":"5.16","versionType":"semver"},{"version":"6.1.175","status":"affected","lessThan":"6.2","versionType":"semver"},{"version":"6.6.141","status":"affected","lessThan":"6.7","versionType":"semver"},{"version":"6.12.91","status":"affected","lessThan":"6.13","versionType":"semver"},{"version":"6.18.33","status":"affected","lessThan":"6.19","versionType":"semver"},{"version":"7.0.10","status":"affected","lessThan":"7.1","versionType":"semver"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["include/linux/nsproxy.h","kernel/fork.c","kernel/nsproxy.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"7.1","status":"affected"},{"version":"0","status":"unaffected","lessThan":"7.1","versionType":"semver"},{"version":"7.2.11","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["include/linux/nsproxy.h","kernel/fork.c","kernel/nsproxy.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/56fe03a0c05dba4c5f6a23c391f96de1614a098c"},{"url":"https://git.kernel.org/stable/c/0b6f31a3c0b16066f812e94b52a704174a6f23cd"}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-23T12:20:00.918Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"7.1","versionEndExcluding":"7.2.11"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"7.1","versionEndExcluding":"7.3"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.15.209"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.1.175"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.6.141"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.12.91"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.18.33"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"7.0.10"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}