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NVD / CVE Program· CNA Linux

CVE-2021-47546: ipv6: fix memory leak in fib6_rule_suppress

Noroxi assessment

Priority: Monitor (action score 22/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.22% (FIRST EPSS).
  • Someone with local access to the system can trigger it. A low-privileged account is enough. No user action is required. No special conditions are required; it is repeatable.
  • Fixed version: Linux Linux 209d35ee34e25f9668c404350a1c86d914c54ffa, 5.3, 5.4.
  • Mentioned 1 time in Turkish national cyber security advisories (siberguvenlik.gov.tr).

Low priority for now. Upgrade to Linux Linux 209d35ee34e25f9668c404350a1c86d914c54ffa, 5.3, 5.4 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

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

MediumCVSS 5.5 · v3.1—No exploit Fix available
Published
May 24, 2024
Updated
Jun 17, 2026
EPSS
0.2% · 12th percentile

Report tools

JSON

Action score

22

Monitor

Low priority for now.

CVSS
22 / 40 · 5.5 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.2%

CISA SSVC decision

Exploitation
none
Automatable
no
Technical impact
partial

Vulnrichment: CISA's decision-tree inputs.

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  • No public exploit code on record
  • A fix has been released

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
linuxlinux kernel

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • linux linux kernel5.4 and later · before 5.4.164
  • linux linux kernel5.5 and later · before 5.10.84
  • linux linux kernel5.11 and later · before 5.15.7

Versions reported by the vendor

Affected version ranges reported by the assigning authority (Linux). Independent of NVD's CPE analysis and usually ahead of it.

  • Linux Linux

    • d37c966752043733eb847dd897d6e3405084c559, ecc265624956ea784cb2bd2b31a95bd54c4f5f13, 5.4affected
    • ca7a03c4175366a92cee0ccc4fec0038c3266e26 and later · before ee38eb8cf9a7323884c2b8e0adbbeb2192d31e29affected · git
    • ca7a03c4175366a92cee0ccc4fec0038c3266e26 and later · before 209d35ee34e25f9668c404350a1c86d914c54ffaaffected · git
    • ca7a03c4175366a92cee0ccc4fec0038c3266e26 and later · before 8ef8a76a340ebdb2c2eea3f6fb0ebbed09a16383affected · git
    • ca7a03c4175366a92cee0ccc4fec0038c3266e26 and later · before cdef485217d30382f3bf6448c54b4401648fe3f1affected · git
    • 5.2.19 and later · before 5.3affected · semver
    • 5.3.4 and later · before 5.4affected · semver
    • before 5.4not affected · semver
    • 5.4.164 and later · up to and including 5.4.*not affected · semver
    • 5.10.84 and later · up to and including 5.10.*not affected · semver

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Debian:12linuxbefore 5.15.15-15.15.15-1
openSUSE:Leap 15.5dtb-aarch64before 5.14.21-150500.55.73.15.14.21-150500.55.73.1
openSUSE:Leap 15.5dtb-aarch64before 5.14.21-150500.55.80.15.14.21-150500.55.80.1
openSUSE:Leap 15.5kernel-64kbbefore 5.14.21-150500.55.80.25.14.21-150500.55.80.2
openSUSE:Leap 15.5kernel-64kbbefore 5.14.21-150500.55.73.15.14.21-150500.55.73.1
openSUSE:Leap 15.5kernel-azurebefore 5.14.21-150500.33.63.15.14.21-150500.33.63.1
openSUSE:Leap 15.5kernel-azurebefore 5.14.21-150500.33.66.15.14.21-150500.33.66.1
openSUSE:Leap 15.5kernel-debugbefore 5.14.21-150500.55.73.15.14.21-150500.55.73.1
openSUSE:Leap 15.5kernel-debugbefore 5.14.21-150500.55.80.25.14.21-150500.55.80.2
openSUSE:Leap 15.5kernel-docsbefore 5.14.21-150500.55.73.25.14.21-150500.55.73.2
openSUSE:Leap 15.5kernel-docsbefore 5.14.21-150500.55.80.25.14.21-150500.55.80.2
openSUSE:Leap 15.5kernel-kvmsmallbefore 5.14.21-150500.55.73.15.14.21-150500.55.73.1
openSUSE:Leap 15.5kernel-kvmsmallbefore 5.14.21-150500.55.80.25.14.21-150500.55.80.2
openSUSE:Leap 15.5kernel-obs-buildbefore 5.14.21-150500.55.80.15.14.21-150500.55.80.1
openSUSE:Leap 15.5kernel-obs-buildbefore 5.14.21-150500.55.73.15.14.21-150500.55.73.1
openSUSE:Leap 15.5kernel-obs-qabefore 5.14.21-150500.55.73.15.14.21-150500.55.73.1
openSUSE:Leap 15.5kernel-obs-qabefore 5.14.21-150500.55.80.15.14.21-150500.55.80.1
openSUSE:Leap 15.5kernel-rt_debugbefore 5.14.21-150500.13.64.15.14.21-150500.13.64.1
openSUSE:Leap 15.5kernel-rt_debugbefore 5.14.21-150500.13.67.35.14.21-150500.13.67.3
openSUSE:Leap 15.5kernel-sourcebefore 5.14.21-150500.55.73.15.14.21-150500.55.73.1
openSUSE:Leap 15.5kernel-sourcebefore 5.14.21-150500.55.80.25.14.21-150500.55.80.2
openSUSE:Leap 15.5kernel-source-azurebefore 5.14.21-150500.33.63.15.14.21-150500.33.63.1
openSUSE:Leap 15.5kernel-source-azurebefore 5.14.21-150500.33.66.15.14.21-150500.33.66.1
openSUSE:Leap 15.5kernel-source-rtbefore 5.14.21-150500.13.67.35.14.21-150500.13.67.3

+49

Same product

linux: all records

Other highest-scoring records for the same primary product.

  • CVE-2026-31431crypto: algif_aead - Revert to operating out-of-placeKEV
    90Now
  • CVE-2022-0847A flaw was found in the way the "flags" member of the new pipe buffer structure was lacking proper initialization in copy_page_to_iter_pipe KEV
    89Now
  • CVE-2021-22555Heap Out-Of-Bounds Write in Netfilter IP6T_SO_SET_REPLACEKEV
    85Now

Published before and after this one in the same product

  • ← EarlierCVE-2021-47542May 24, 2024 · net: qlogic: qlcnic: Fix a NULL pointer dereference in qlcnic_83xx_add_rings()
    22Monitor
  • ← EarlierCVE-2021-47544May 24, 2024 · tcp: fix page frag corruption on page fault
    23Monitor
  • Later →CVE-2021-47547May 24, 2024 · net: tulip: de4x5: fix the problem that the array 'lp->phy[8]' may be out of bound
    17Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
Linux Linux209d35ee34e25f9668c404350a1c86d914c54ffaVendor (CNA)
Linux Linux5.3Vendor (CNA)
Linux Linux5.4Vendor (CNA)
Linux Linux8ef8a76a340ebdb2c2eea3f6fb0ebbed09a16383Vendor (CNA)
Linux Linuxcdef485217d30382f3bf6448c54b4401648fe3f1Vendor (CNA)
Linux Linuxee38eb8cf9a7323884c2b8e0adbbeb2192d31e29Vendor (CNA)
debian:linux5.15.15-1 · Debian:12Package registry (OSV)
opensuse:dtb-aarch645.14.21-150500.55.73.1 · openSUSE:Leap 15.5Package registry (OSV)
opensuse:kernel-64kb5.14.21-150500.55.73.1 · openSUSE:Leap 15.5Package registry (OSV)
opensuse:kernel-debug5.14.21-150500.55.73.1 · openSUSE:Leap 15.5Package registry (OSV)
opensuse:kernel-default5.14.21-150500.55.73.1 · openSUSE:Leap Micro 5.5Package registry (OSV)
opensuse:kernel-default-base5.14.21-150500.55.73.1.150500.6.33.8 · openSUSE:Leap Micro 5.5Package registry (OSV)
opensuse:kernel-docs5.14.21-150500.55.73.2 · openSUSE:Leap 15.5Package registry (OSV)
opensuse:kernel-kvmsmall5.14.21-150500.55.73.1 · openSUSE:Leap 15.5Package registry (OSV)
opensuse:kernel-obs-build5.14.21-150500.55.73.1 · openSUSE:Leap 15.5Package registry (OSV)
opensuse:kernel-rt5.14.21-150500.13.64.1 · openSUSE:Leap Micro 5.5Package registry (OSV)
opensuse:kernel-rt_debug5.14.21-150500.13.64.1 · openSUSE:Leap 15.5Package registry (OSV)
opensuse:kernel-source-rt5.14.21-150500.13.64.1 · openSUSE:Leap 15.5Package registry (OSV)
opensuse:kernel-syms-rt5.14.21-150500.13.64.1 · openSUSE:Leap 15.5Package registry (OSV)
suse:kernel-64kb5.14.21-150500.55.73.1 · SUSE:Linux Enterprise Module for Basesystem 15 SP5Package registry (OSV)
suse:kernel-default5.14.21-150500.55.73.1 · SUSE:Linux Enterprise Micro 5.5Package registry (OSV)
suse:kernel-default-base5.14.21-150500.55.73.1.150500.6.33.8 · SUSE:Linux Enterprise Micro 5.5Package registry (OSV)
suse:kernel-docs5.14.21-150500.55.73.2 · SUSE:Linux Enterprise Module for Development Tools 15 SP5Package registry (OSV)
suse:kernel-livepatch-SLE15-SP5-RT_Update_181-150500.11.3.1 · SUSE:Linux Enterprise Live Patching 15 SP5Package registry (OSV)
suse:kernel-obs-build5.14.21-150500.55.73.1 · SUSE:Linux Enterprise Module for Development Tools 15 SP5Package registry (OSV)
suse:kernel-rt5.14.21-150500.13.64.1 · SUSE:Linux Enterprise Micro 5.5Package registry (OSV)
suse:kernel-rt_debug5.14.21-150500.13.64.1 · SUSE:Real Time Module 15 SP5Package registry (OSV)
suse:kernel-source5.14.21-150500.55.73.1 · SUSE:Linux Enterprise Module for Basesystem 15 SP5Package registry (OSV)
suse:kernel-source-rt5.14.21-150500.13.64.1 · SUSE:Linux Enterprise Micro 5.5Package registry (OSV)
suse:kernel-syms-rt5.14.21-150500.13.64.1 · SUSE:Real Time Module 15 SP5Package registry (OSV)

+1

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

National notice (Türkiye Cybersecurity Directorate / USOM)

Official security notices citing this record; remediation advice is on the agency's page.

All national notices →

Technical details

Attack conditions

  • Someone with local access to the system can trigger it.
  • A low-privileged account is enough.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
none
Integrity
none
Availability
high · the service can be disrupted
Attack vector
Local
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality impact
None
Integrity impact
None
Availability impact
High

Weakness class (CWE)

CWE-401 · Missing Release of Memory after Effective Lifetime

CVSS vector

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

nvd-primary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Show all references (3 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records