CVE-2021-47546

Service interruption via IPv6 route reference leak

Published May 24, 2024 · Updated May 23, 2026

Memory leak in Linux IPv6 routing allows local users to exhaust kernel memory by sending IPv6 traffic to a specially configured host. fib6_rule_suppress checks the always-set generic FIB_LOOKUP_NOREF flag instead of RT6_LOOKUP_F_DST_NOREF, so some ip6_dst_cache references are never released. The leak requires an IPv6 nftables fib rule and a suppress_prefix routing rule; every incoming IPv6 packet then consumes another allocation and can interrupt service.

CVSS severity5.5
Medium
EPSS probability0.22%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Memory leak in Linux IPv6 routing allows local users to exhaust kernel memory by sending IPv6 traffic to a specially configured host. fib6_rule_suppress checks the always-set generic FIB_LOOKUP_NOREF flag instead of RT6_LOOKUP_F_DST_NOREF, so some ip6_dst_cache references are never released. The leak requires an IPv6 nftables fib rule and a suppress_prefix routing rule; every incoming IPv6 packet then consumes another allocation and can interrupt service.

The record

CVE
CVE-2021-47546
Published
May 24, 2024
Updated
May 23, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
T1499.004
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. May 24, 2024CVE publishedPublication date reported by the CVE source.
  2. May 23, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=5.2.19 <5.3
  2. Affected versionversion=5.3.4 <5.4
  3. Affected versionversion=5.4
  4. Affected versionversion=ca7a03c4175366a92cee0ccc4fec0038c3266e26 <209d35ee34e25f9668c404350a1c86d914c54ffa
  5. Affected versionversion=ca7a03c4175366a92cee0ccc4fec0038c3266e26 <8ef8a76a340ebdb2c2eea3f6fb0ebbed09a16383
  6. Affected versionversion=ca7a03c4175366a92cee0ccc4fec0038c3266e26 <cdef485217d30382f3bf6448c54b4401648fe3f1
  7. Affected versionversion=ca7a03c4175366a92cee0ccc4fec0038c3266e26 <ee38eb8cf9a7323884c2b8e0adbbeb2192d31e29
  8. Affected versionversion=d37c966752043733eb847dd897d6e3405084c559
  9. Affected versionversion=ecc265624956ea784cb2bd2b31a95bd54c4f5f13

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=5.2.19 <5.3; version=5.3.4 <5.4; version=5.4; version=ca7a03c4175366a92cee0ccc4fec0038c3266e26 <209d35ee34e25f9668c404350a1c86d914c54ffa; version=ca7a03c4175366a92cee0ccc4fec0038c3266e26 <8ef8a76a340ebdb2c2eea3f6fb0ebbed09a16383; version=ca7a03c4175366a92cee0ccc4fec0038c3266e26 <cdef485217d30382f3bf6448c54b4401648fe3f1; version=ca7a03c4175366a92cee0ccc4fec0038c3266e26 <ee38eb8cf9a7323884c2b8e0adbbeb2192d31e29; version=d37c966752043733eb847dd897d6e3405084c559; version=ecc265624956ea784cb2bd2b31a95bd54c4f5f13

Published CVSS scores

5.5CanonicalCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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