---
id: "CVE-2026-99112"
kind: "vulnerability"
aliases: ["CVE-2026-99112"]
title: "Linux kernel: flower tunnel-option mask parsing reads past its buffer"
severity: "unknown"
cvss: null
epss: null
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["cls-flower", "linux-kernel", "net-sched", "runtime"]
not_affected_if: ["kernel-without-cls-flower"]
published_at: "2026-10-28T11:17:30+00:00"
first_seen_at: "2026-10-28T11:32:34+00:00"
updated_at: "2026-10-28T11:37:43+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-99112", "first_seen_at": "2026-10-28T11:32:34+00:00"}]
---

# Linux kernel: flower tunnel-option mask parsing reads past its buffer

A malformed tc flower filter with tunnel-option mask data that is not a complete netlink attribute makes the kernel read beyond the mask payload while parsing it. The sources describe this as an out-of-bounds read, and the fix rejects such filters with -EINVAL.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Run `uname -r` and compare with the fixed kernel version in the upstream commit, which the sources do not name.
- unknown

## Fix

- Install a Linux kernel build that includes the fix for CVE-2026-99112, once your distribution publishes it.
- unknown

## Timeline

- 2026-10-28T11:32:34+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-99112

## From the sources

In the Linux kernel, the following vulnerability has been resolved:

net/sched: cls_flower: validate mask pointer after nla_next()

fl_set_enc_opt() iterates the key's nested tunnel-option attributes
with nla_for_each_attr() while advancing a single mask pointer via
nla_next() at the bottom of each loop, so the mask cursor is driven
by the number of key attributes rather than by the mask's own
attributes.  The nla_ok() added by commit c96adff956191 ("cls_flower:
call nla_ok() before nla_next()") only validates the mask pointer
that was just consumed; the pointer produced by nla_next() is used by
the next iteration (fl_set_geneve_opt() and siblings) without any
validation.

The mask's nested attributes are validated with NL_VALIDATE_LIBERAL,
which merely warns on trailing bytes that do not form a complete
attribute.  A mask carrying one valid attribute plus 1-3 residue
bytes (or a non-aligned attribute length making msk_depth negative)
therefore reaches the next iteration with msk_depth != 0, so neither
the !msk_depth check in fl_set_enc_opt() nor the !depth check in the
per-type helpers fires.  nla_type() then reads past the mask payload
and nla_parse_nested_deprecated() iterates with an nla_len taken
from those bytes, reading well beyond the mask attribute (KASAN:
slab-out-of-bounds read in __nla_validate_parse from fl_change()).

Validate the advanced mask pointer as well: when the mask is not
legitimately exhausted (msk_depth != 0) and the new pointer fails
nla_ok(), reject the filter with -EINVAL.  An exactly exhausted mask
still skips the check, preserving exact-match behaviour for the
remaining key attributes.

---

_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_