{"id":"AZL-106307","summary":"CVE-2026-98299 affecting package kernel 6.6.157.1-1","details":"In the Linux kernel, the following vulnerability has been resolved:\n\ntcp: do not let tcp_rmem be set below 4096\n\nWe can hit a division by zero crash in tcp_rcvbuf_grow()\nand tcp_rcv_space_adjust():\n\ndivide error: 0000 [#1] PREEMPT SMP\nRIP: 0010:tcp_rcvbuf_grow+0x187/0x450 net/ipv4/tcp_input.c:939\n...\ngrow = div_u64(((u64)rcvwin \u003c\u003c 1) * (newval - oldval), oldval);\n\nThe division uses oldval = tp-\u003ercvq_space.space as divisor.\nWhen tp-\u003ercvq_space.space is zero, this leads to a divide-by-zero\nexception.\n\ntp-\u003ercvq_space.space is initialized in tcp_init_buffer_space():\n    tp-\u003ercvq_space.space = min3(tp-\u003ercv_ssthresh, tp-\u003ercv_wnd,\n                                (u32)TCP_INIT_CWND * tp-\u003eadvmss);\n\nIf tcp_rmem[1] is configured to very small values (such as 1),\nsk-\u003esk_rcvbuf is initialized to 1. Then tcp_full_space(sk), which\ncomputes (sk-\u003esk_rcvbuf * scaling_ratio) \u003e\u003e 8, truncates to 0.\nThis sets tp-\u003ewindow_clamp = 0, tp-\u003ercv_ssthresh = 0, and\ntp-\u003ercvq_space.space = 0. Later, when data arrives and DRS is invoked,\ntcp_rcvbuf_grow() divides by oldval == 0.\n\nBack in 2015, commit b1cb59cf2efe (\"net: sysctl_net_core: check SNDBUF\nand RCVBUF for min length\") ensured that net.core.rmem_default and\nnet.core.rmem_max cannot be set below SOCK_MIN_RCVBUF. Similarly,\nSO_RCVBUF setsockopt enforces max_t(int, val * 2, SOCK_MIN_RCVBUF).\n\nHowever, net.ipv4.tcp_rmem still had .extra1 = SYSCTL_ONE, allowing\narbitrarily small values.\n\nBecause SOCK_MIN_RCVBUF depends on sizeof(struct sk_buff) and cacheline\nalignment, its value varies across architectures and configuration options.\nUsing a fixed constant of 4096 ensures a predictable, architecture-\nindependent lower bound that is safely above SOCK_MIN_RCVBUF everywhere\nand matches the documented 4K default.\n\nFix this by setting tcp_rmem.extra1 to 4096 and updating the documentation.","modified":"2026-10-07T14:17:01.487399077Z","published":"2026-10-06T09:18:20Z","upstream":["CVE-2026-98299"],"references":[{"type":"WEB","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-98299"}],"affected":[{"package":{"name":"kernel","ecosystem":"Azure Linux:3","purl":"pkg:rpm/azure-linux/kernel"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"last_affected":"6.6.157.1-1"}]}],"database_specific":{"source":"https://github.com/microsoft/AzureLinuxVulnerabilityData/blob/main/osv/AZL-106307.json"}}],"schema_version":"1.9.0"}