{"id":"CVE-2026-74577","summary":"net: mpls: initialize rtm_tos in mpls_getroute()","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet: mpls: initialize rtm_tos in mpls_getroute()\n\nmpls_getroute() builds the RTM_NEWROUTE reply to an RTM_GETROUTE\nrequest by filling a struct rtmsg allocated from an skb whose data\narea is not zeroed (alloc_skb(NLMSG_GOODSIZE, ...)). It sets every\nfield of the header except rtm_tos:\n\n\tr = nlmsg_data(nlh);\n\tr-\u003ertm_family\t = AF_MPLS;\n\tr-\u003ertm_dst_len\t= 20;\n\tr-\u003ertm_src_len\t= 0;\n\tr-\u003ertm_table\t= RT_TABLE_MAIN;\n\tr-\u003ertm_type\t= RTN_UNICAST;\n\tr-\u003ertm_scope\t= RT_SCOPE_UNIVERSE;\n\tr-\u003ertm_protocol = rt-\u003ert_protocol;\n\tr-\u003ertm_flags\t= 0;\n\nstruct rtmsg has no padding, so the one uninitialised byte rtm_tos\n(offset 3) is copied straight to user space on recvmsg(), leaking a\nbyte of uninitialised heap memory. This is in contrast to\nmpls_dump_route(), which fills the very same header and does set\nrtm_tos = 0.\n\nInitialize rtm_tos to 0, matching mpls_dump_route().\n\nReproduced with KMSAN by adding an MPLS route and issuing a\nnon-RTM_F_FIB_MATCH RTM_GETROUTE for its label:\n\n  BUG: KMSAN: kernel-infoleak in _copy_to_iter+0x36c/0x33f0\n   _copy_to_iter+0x36c/0x33f0\n   __skb_datagram_iter+0x196/0x12c0\n   skb_copy_datagram_iter+0x5b/0x210\n   netlink_recvmsg+0x37b/0xef0\n   ...\n  Uninit was created at:\n   __alloc_skb+0x8ca/0x10e0\n   mpls_getroute+0x1280/0x3a40\n   rtnetlink_rcv_msg+0x1138/0x15a0\n   ...\n  Byte 19 of 64 is uninitialized\n\n(byte 19 = nlmsghdr(16) + rtmsg offset 3 = rtm_tos)","modified":"2026-08-20T03:55:17.324095586Z","published":"2026-08-15T12:28:14.408Z","database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/74xxx/CVE-2026-74577.json"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/1fea5ff0eb4aa7e951bb3d380248566c473aa377"},{"type":"WEB","url":"https://git.kernel.org/stable/c/248718fd88b146d8bdc7610ecd1eb4cd16e0b5a1"},{"type":"WEB","url":"https://git.kernel.org/stable/c/295dd295e2137e10e9a5b1891d97e0f08de76f03"},{"type":"WEB","url":"https://git.kernel.org/stable/c/2dc2fffc704a4365cae1aae078ba62223aaeff93"},{"type":"WEB","url":"https://git.kernel.org/stable/c/466b474a8deb0c93b5280c6d261e5eda6482eca7"},{"type":"WEB","url":"https://git.kernel.org/stable/c/95651461cf77cc6590fa08c87667717e5dcfa55d"},{"type":"WEB","url":"https://git.kernel.org/stable/c/a5cdd2407dd890f741f59b8367e4c6c101cce154"},{"type":"WEB","url":"https://git.kernel.org/stable/c/ba56f88aab18d982f2a21f11390f4d8a8897782a"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/74xxx/CVE-2026-74577.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-74577"},{"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":"397fc9e5cefee0c33b86811fbddb0decb7288c52"},{"fixed":"248718fd88b146d8bdc7610ecd1eb4cd16e0b5a1"},{"fixed":"466b474a8deb0c93b5280c6d261e5eda6482eca7"},{"fixed":"ba56f88aab18d982f2a21f11390f4d8a8897782a"},{"fixed":"95651461cf77cc6590fa08c87667717e5dcfa55d"},{"fixed":"1fea5ff0eb4aa7e951bb3d380248566c473aa377"},{"fixed":"a5cdd2407dd890f741f59b8367e4c6c101cce154"},{"fixed":"2dc2fffc704a4365cae1aae078ba62223aaeff93"},{"fixed":"295dd295e2137e10e9a5b1891d97e0f08de76f03"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-74577.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"4.13.0"},{"fixed":"5.10.265"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.11.0"},{"fixed":"5.15.216"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.16.0"},{"fixed":"6.1.183"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.2.0"},{"fixed":"6.6.151"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.7.0"},{"fixed":"6.12.103"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.18.44"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"7.1.8"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-74577.json"}}],"schema_version":"1.9.0"}