{"id":"DEBIAN-CVE-2026-74577","details":"In the Linux kernel, the following vulnerability has been resolved:  net: mpls: initialize rtm_tos in mpls_getroute()  mpls_getroute() builds the RTM_NEWROUTE reply to an RTM_GETROUTE request by filling a struct rtmsg allocated from an skb whose data area is not zeroed (alloc_skb(NLMSG_GOODSIZE, ...)). It sets every field of the header except rtm_tos:  \tr = nlmsg_data(nlh); \tr-\u003ertm_family\t = AF_MPLS; \tr-\u003ertm_dst_len\t= 20; \tr-\u003ertm_src_len\t= 0; \tr-\u003ertm_table\t= RT_TABLE_MAIN; \tr-\u003ertm_type\t= RTN_UNICAST; \tr-\u003ertm_scope\t= RT_SCOPE_UNIVERSE; \tr-\u003ertm_protocol = rt-\u003ert_protocol; \tr-\u003ertm_flags\t= 0;  struct rtmsg has no padding, so the one uninitialised byte rtm_tos (offset 3) is copied straight to user space on recvmsg(), leaking a byte of uninitialised heap memory. This is in contrast to mpls_dump_route(), which fills the very same header and does set rtm_tos = 0.  Initialize rtm_tos to 0, matching mpls_dump_route().  Reproduced with KMSAN by adding an MPLS route and issuing a non-RTM_F_FIB_MATCH RTM_GETROUTE for its label:    BUG: KMSAN: kernel-infoleak in _copy_to_iter+0x36c/0x33f0    _copy_to_iter+0x36c/0x33f0    __skb_datagram_iter+0x196/0x12c0    skb_copy_datagram_iter+0x5b/0x210    netlink_recvmsg+0x37b/0xef0    ...   Uninit was created at:    __alloc_skb+0x8ca/0x10e0    mpls_getroute+0x1280/0x3a40    rtnetlink_rcv_msg+0x1138/0x15a0    ...   Byte 19 of 64 is uninitialized  (byte 19 = nlmsghdr(16) + rtmsg offset 3 = rtm_tos)","modified":"2026-09-19T22:02:34.326841543Z","published":"2026-08-15T13:18:03.430Z","upstream":["CVE-2026-74577"],"references":[{"type":"ADVISORY","url":"https://security-tracker.debian.org/tracker/CVE-2026-74577"}],"affected":[{"package":{"name":"linux","ecosystem":"Debian:12","purl":"pkg:deb/debian/linux?arch=source&distro=bookworm"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"6.1.187-1"}]}],"versions":["6.1.106-1","6.1.106-2","6.1.106-3","6.1.112-1","6.1.115-1","6.1.119-1","6.1.123-1","6.1.124-1","6.1.128-1","6.1.129-1","6.1.133-1","6.1.135-1","6.1.137-1","6.1.139-1","6.1.140-1","6.1.147-1","6.1.148-1","6.1.153-1","6.1.158-1","6.1.159-1","6.1.162-1","6.1.164-1","6.1.170-1","6.1.170-2","6.1.170-3","6.1.172-1","6.1.174-1","6.1.176-1","6.1.177-1","6.1.180-1","6.1.27-1","6.1.37-1","6.1.38-1","6.1.38-2","6.1.38-2~bpo11+1","6.1.38-3","6.1.38-4","6.1.38-4~bpo11+1","6.1.52-1","6.1.55-1","6.1.55-1~bpo11+1","6.1.64-1","6.1.66-1","6.1.67-1","6.1.69-1","6.1.69-1~bpo11+1","6.1.76-1","6.1.76-1~bpo11+1","6.1.82-1","6.1.85-1","6.1.90-1","6.1.90-1~bpo11+1","6.1.94-1","6.1.94-1~bpo11+1","6.1.98-1","6.1.99-1"],"ecosystem_specific":{"urgency":"not 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