CVE-2021-47546

Advisory lineage Upstream: 0 Downstream: 8
Modified
Published: 24 May 2024, 15:09
Last modified:23 May 2026, 15:20

Vulnerability Summary

Overall Risk (default)
low
22/100
CVSS Score
5.5 MEDIUM
v3.1 (nvd)
EPSS Score
0.01% LOW
0% probability 0.00%
KEV
Not listed
Ransomware
No reports
Public exploits
None found
Dark Web
Not detected

Timeline

24 May 2024, 15:09
Published
Vulnerability first disclosed
23 May 2026, 15:20
Last Modified
Vulnerability information updated

Description

In the Linux kernel, the following vulnerability has been resolved: ipv6: fix memory leak in fib6_rule_suppress The kernel leaks memory when a `fib` rule is present in IPv6 nftables firewall rules and a suppress_prefix rule is present in the IPv6 routing rules (used by certain tools such as wg-quick). In such scenarios, every incoming packet will leak an allocation in `ip6_dst_cache` slab cache. After some hours of `bpftrace`-ing and source code reading, I tracked down the issue to ca7a03c41753 ("ipv6: do not free rt if FIB_LOOKUP_NOREF is set on suppress rule"). The problem with that change is that the generic `args->flags` always have `FIB_LOOKUP_NOREF` set[1][2] but the IPv6-specific flag `RT6_LOOKUP_F_DST_NOREF` might not be, leading to `fib6_rule_suppress` not decreasing the refcount when needed. How to reproduce: - Add the following nftables rule to a prerouting chain: meta nfproto ipv6 fib saddr . mark . iif oif missing drop This can be done with: sudo nft create table inet test sudo nft create chain inet test test_chain '{ type filter hook prerouting priority filter + 10; policy accept; }' sudo nft add rule inet test test_chain meta nfproto ipv6 fib saddr . mark . iif oif missing drop - Run: sudo ip -6 rule add table main suppress_prefixlength 0 - Watch `sudo slabtop -o | grep ip6_dst_cache` to see memory usage increase with every incoming ipv6 packet. This patch exposes the protocol-specific flags to the protocol specific `suppress` function, and check the protocol-specific `flags` argument for RT6_LOOKUP_F_DST_NOREF instead of the generic FIB_LOOKUP_NOREF when decreasing the refcount, like this. [1]: https://github.com/torvalds/linux/blob/ca7a03c4175366a92cee0ccc4fec0038c3266e26/net/ipv6/fib6_rules.c#L71 [2]: https://github.com/torvalds/linux/blob/ca7a03c4175366a92cee0ccc4fec0038c3266e26/net/ipv6/fib6_rules.c#L99

CVSS Metrics

  • v3.1•MEDIUM•Score: 5.5CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

EPSS Trends

Current EPSS score: 0.01%• Percentile: 3%

Techniques & Countermeasures

  • CWE-401•Missing Release of Memory after Effective Lifetime

    The product does not sufficiently track and release allocated memory after it has been used, making the memory unavailable for reallocation and reuse.

Affected Systems

  • linux•linux

    ≥ ca7a03c4175366a92cee0ccc4fec0038c3266e26, < ee38eb8cf9a7323884c2b8e0adbbeb2192d31e29 | ≥ ca7a03c4175366a92cee0ccc4fec0038c3266e26, < 209d35ee34e25f9668c404350a1c86d914c54ffa | ≥ ca7a03c4175366a92cee0ccc4fec0038c3266e26, < 8ef8a76a340ebdb2c2eea3f6fb0ebbed09a16383 | ≥ ca7a03c4175366a92cee0ccc4fec0038c3266e26, < cdef485217d30382f3bf6448c54b4401648fe3f1 | d37c966752043733eb847dd897d6e3405084c559 | ecc265624956ea784cb2bd2b31a95bd54c4f5f13 | ≥ 5.2.19, < 5.3 | ≥ 5.3.4, < 5.4 | 5.4

  • linux•linux_kernel

    ≥ 5.4, < 5.4.164 | ≥ 5.5, < 5.10.84 | ≥ 5.11, < 5.15.7

References (4)