{"cve":"CVE-2026-98299","nvd":{"published":"2026-10-06T09:18:20.697","modified":"2026-10-19T10:18:31.743","status":"Received","description":"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 << 1) * (newval - oldval), oldval);\n\nThe division uses oldval = tp->rcvq_space.space as divisor.\nWhen tp->rcvq_space.space is zero, this leads to a divide-by-zero\nexception.\n\ntp->rcvq_space.space is initialized in tcp_init_buffer_space():\n    tp->rcvq_space.space = min3(tp->rcv_ssthresh, tp->rcv_wnd,\n                                (u32)TCP_INIT_CWND * tp->advmss);\n\nIf tcp_rmem[1] is configured to very small values (such as 1),\nsk->sk_rcvbuf is initialized to 1. Then tcp_full_space(sk), which\ncomputes (sk->sk_rcvbuf * scaling_ratio) >> 8, truncates to 0.\nThis sets tp->window_clamp = 0, tp->rcv_ssthresh = 0, and\ntp->rcvq_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.","cvss_v4":null,"cvss_v3":null,"cwes":[],"references":["https://git.kernel.org/stable/c/1c4bb940c3bb4325bb88ac1b7eaf5faaa39e7d63","https://git.kernel.org/stable/c/60df201dbb19a1bf6478b56d100f7ae1fe90e46a","https://git.kernel.org/stable/c/67b83c15bed9eeeb8d1a6dbf88a5f79525970173","https://git.kernel.org/stable/c/7898bda1ebc198f5559b301a96dd5398edd4d4d3","https://git.kernel.org/stable/c/83a945a529d6e002dd7339c532288a931f463dba"],"products":[],"source":"nvd","synced_at":"2026-10-19T22:57:46.668721662+00:00"},"epss":{"cve":"CVE-2026-98299","score":0.00177,"percentile":0.07149,"date":"2026-10-25"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}