{
  "cveId": "CVE-2021-47546",
  "url": "https://patchblox.com/security/cve/CVE-2021-47546",
  "summary": "CVE-2021-47546 is fixed in linux on 1 platform, first by DEBIAN-CVE-2021-47546, released May 24, 2024. It is not reported as exploited. Patch Radar priority: Routine.",
  "title": "linux: In the Linux kernel, the following vulnerability has been resolved:  ipv6: fix memory leak in fib6_rule_suppress  The...",
  "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 \u0060fib\u0060 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 \u0060ip6_dst_cache\u0060 slab cache.  After some hours of \u0060bpftrace\u0060-ing and source code reading, I tracked down the issue to ca7a03c41753 (\u0022ipv6: do not free rt if FIB_LOOKUP_NOREF is set on suppress rule\u0022).  The problem with that change is that the generic \u0060args-\u003Eflags\u0060 always have \u0060FIB_LOOKUP_NOREF\u0060 set[1][2] but the IPv6-specific flag \u0060RT6_LOOKUP_F_DST_NOREF\u0060 might not be, leading to \u0060fib6_rule_suppress\u0060 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 \u0027{ type filter hook prerouting priority filter \u002B 10; policy accept; }\u0027      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 \u0060sudo slabtop -o | grep ip6_dst_cache\u0060 to see memory usage increase    with every incoming ipv6 packet.  This patch exposes the protocol-specific flags to the protocol specific \u0060suppress\u0060 function, and check the protocol-specific \u0060flags\u0060 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",
  "published": "2024-05-24T15:15:19Z",
  "severity": "medium",
  "cvss": 5.5,
  "cvssVector": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
  "epss": 0.00222,
  "epssPercentile": 0.12853,
  "priority": "Routine",
  "priorityTier": 4,
  "exploited": false,
  "vendorExploited": false,
  "disclosed": false,
  "fixes": [
    {
      "platform": "linux",
      "product": "linux",
      "release": "Debian 12.15 (bookworm)",
      "fixedVersion": "5.15.15-1",
      "fix": "DEBIAN-CVE-2021-47546",
      "url": "https://patchblox.com/security/fix/linux/debian-cve-2021-47546",
      "released": "2024-05-24T15:15:19Z"
    },
    {
      "platform": "linux",
      "product": "linux",
      "release": "Debian 13.5 (trixie)",
      "fixedVersion": "5.15.15-1",
      "fix": "DEBIAN-CVE-2021-47546",
      "url": "https://patchblox.com/security/fix/linux/debian-cve-2021-47546",
      "released": "2024-05-24T15:15:19Z"
    },
    {
      "platform": "linux",
      "product": "linux",
      "release": "Debian 14",
      "fixedVersion": "5.15.15-1",
      "fix": "DEBIAN-CVE-2021-47546",
      "url": "https://patchblox.com/security/fix/linux/debian-cve-2021-47546",
      "released": "2024-05-24T15:15:19Z"
    }
  ],
  "noFixYet": [],
  "dataAsOf": "2026-11-08T13:06:02Z",
  "attribution": {
    "text": "Data: Patchblox Patch Radar",
    "url": "https://patchblox.com/security/patch-radar",
    "terms": "https://patchblox.com/security/patch-radar/use-the-data"
  }
}