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NVD / CVE Program· CNA Linux

CVE-2021-47515: seg6: fix the iif in the IPv6 socket control block

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: 0.74% (FIRST EPSS); higher than 55.1% of all records.
  • 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 4.14.258, 4.19.221, 4.21.
  • Severity is disputed: the assigning authority (CNA) scores it 7.5, NVD 5.5.
  • Mentioned 1 time in Turkish national cyber security advisories (siberguvenlik.gov.tr).

Low priority for now. Upgrade to Linux Linux 4.14.258, 4.19.221, 4.21 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: seg6: fix the iif in the IPv6 socket control block When an IPv4 packet is received, the ip_rcv_core(...) sets the receiving interface index into the IPv4 socket control block (v5.16-rc4, net/ipv4/ip_input.c line 510): IPCB(skb)->iif = skb->skb_iif; If that IPv4 packet is meant to be encapsulated in an outer IPv6+SRH header, the seg6_do_srh_encap(...) performs the required encapsulation. In this case, the seg6_do_srh_encap function clears the IPv6 socket control block (v5.16-rc4 net/ipv6/seg6_iptunnel.c line 163): memset(IP6CB(skb), 0, sizeof(*IP6CB(skb))); The memset(...) was introduced in commit ef489749aae5 ("ipv6: sr: clear IP6CB(skb) on SRH ip4ip6 encapsulation") a long time ago (2019-01-29). Since the IPv6 socket control block and the IPv4 socket control block share the same memory area (skb->cb), the receiving interface index info is lost (IP6CB(skb)->iif is set to zero). As a side effect, that condition triggers a NULL pointer dereference if commit 0857d6f8c759 ("ipv6: When forwarding count rx stats on the orig netdev") is applied. To fix that issue, we set the IP6CB(skb)->iif with the index of the receiving interface once again.

MediumCVSS 5.5 · v3.1—No exploit Fix available
Published
May 24, 2024
Updated
Aug 5, 2026
EPSS
0.7% · 55th 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 · 0.7%

CISA SSVC decision

Exploitation
none
Automatable
no
Technical impact
partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
5.5
CNA · Linux
7.5
2.0 point gap

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

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

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  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

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Noroxi analysis

What does it mean in your environment?

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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 kernel4.14.98 and later · before 4.14.258
  • linux linux kernel4.19.20 and later · before 4.19.221
  • linux linux kernel4.20.7 and later · before 5.0
  • linux linux kernel5.0.1 and later · before 5.4.165
  • linux linux kernel5.5 and later · before 5.10.85
  • linux linux kernel5.11 and later · before 5.15.8
  • linux linux kernel5.0
  • linux linux kernel5.16

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

    • b71b7e0280f47b4ac633fbfd153423814ea87810, 5.0affected
    • c630ec8bdadae9d557b1ceb9d6c06e149108a0d4 and later · before b16d412e5f79734033df04e97d7ea2f50a8e9fe3affected · git
    • 2f704348c93ff8119e642dae6a72327f90b82810 and later · before 6431e71093f3da586a00c6d931481ffb0dc2db0eaffected · git
    • ef489749aae508e6f17886775c075f12ff919fb1 and later · before ef8804e47c0a44ae106ead1740408af5ea6c6ee9affected · git
    • ef489749aae508e6f17886775c075f12ff919fb1 and later · before 666521b3852d2b2f52d570f9122b1e4b50d96831affected · git
    • ef489749aae508e6f17886775c075f12ff919fb1 and later · before 98adb2bbfa407c9290bda299d4c6f7a1c4ebd5e1affected · git
    • ef489749aae508e6f17886775c075f12ff919fb1 and later · before ae68d93354e5bf5191ee673982251864ea24dd5caffected · git
    • 4.14.98 and later · before 4.14.258affected · semver
    • 4.19.20 and later · before 4.19.221affected · semver
    • 4.20.7 and later · before 4.21affected · 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 15.5kernel-64kbbefore 5.14.21-150500.55.73.15.14.21-150500.55.73.1
openSUSE:Leap 15.5kernel-azurebefore 5.14.21-150500.33.60.15.14.21-150500.33.60.1
openSUSE:Leap 15.5kernel-debugbefore 5.14.21-150500.55.73.15.14.21-150500.55.73.1
openSUSE:Leap 15.5kernel-docsbefore 5.14.21-150500.55.73.25.14.21-150500.55.73.2
openSUSE:Leap 15.5kernel-kvmsmallbefore 5.14.21-150500.55.73.15.14.21-150500.55.73.1
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-rtbefore 5.14.21-150500.13.61.15.14.21-150500.13.61.1
openSUSE:Leap 15.5kernel-rt_debugbefore 5.14.21-150500.13.61.15.14.21-150500.13.61.1
openSUSE:Leap 15.5kernel-sourcebefore 5.14.21-150500.55.73.15.14.21-150500.55.73.1
openSUSE:Leap 15.5kernel-source-azurebefore 5.14.21-150500.33.60.15.14.21-150500.33.60.1
openSUSE:Leap 15.5kernel-source-rtbefore 5.14.21-150500.13.61.15.14.21-150500.13.61.1
openSUSE:Leap 15.5kernel-symsbefore 5.14.21-150500.55.73.15.14.21-150500.55.73.1
openSUSE:Leap 15.5kernel-syms-azurebefore 5.14.21-150500.33.60.15.14.21-150500.33.60.1
openSUSE:Leap 15.5kernel-syms-rtbefore 5.14.21-150500.13.61.15.14.21-150500.13.61.1
openSUSE:Leap 15.5kernel-zfcpdumpbefore 5.14.21-150500.55.73.15.14.21-150500.55.73.1
openSUSE:Leap Micro 5.5kernel-defaultbefore 5.14.21-150500.55.73.15.14.21-150500.55.73.1
openSUSE:Leap Micro 5.5kernel-default-basebefore 5.14.21-150500.55.73.1.150500.6.33.85.14.21-150500.55.73.1.150500.6.33.8
Red Hat:enterprise_linux:9::appstreambpftool-debuginfobefore 0:7.2.0-362.8.1.el9_30:7.2.0-362.8.1.el9_3
Red Hat:enterprise_linux:9::appstreamkernel-64k-debug-debuginfobefore 0:5.14.0-362.8.1.el9_30:5.14.0-362.8.1.el9_3
Red Hat:enterprise_linux:9::appstreamkernel-64k-debug-develbefore 0:5.14.0-362.8.1.el9_30:5.14.0-362.8.1.el9_3
Red Hat:enterprise_linux:9::appstreamkernel-64k-debug-devel-matchedbefore 0:5.14.0-362.8.1.el9_30:5.14.0-362.8.1.el9_3

+91

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-2021-47513May 24, 2024 · net: dsa: felix: Fix memory leak in felix_setup_mmio_filtering
    22Monitor
  • ← EarlierCVE-2021-47514May 24, 2024 · devlink: fix netns refcount leak in devlink_nl_cmd_reload()
    22Monitor
  • Later →CVE-2021-47516May 24, 2024 · nfp: Fix memory leak in nfp_cpp_area_cache_add()
    22Monitor

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 Linux4.14.258Vendor (CNA)
Linux Linux4.19.221Vendor (CNA)
Linux Linux4.21Vendor (CNA)
Linux Linux6431e71093f3da586a00c6d931481ffb0dc2db0eVendor (CNA)
Linux Linux666521b3852d2b2f52d570f9122b1e4b50d96831Vendor (CNA)
Linux Linux98adb2bbfa407c9290bda299d4c6f7a1c4ebd5e1Vendor (CNA)
Linux Linuxae68d93354e5bf5191ee673982251864ea24dd5cVendor (CNA)
Linux Linuxb16d412e5f79734033df04e97d7ea2f50a8e9fe3Vendor (CNA)
Linux Linuxef8804e47c0a44ae106ead1740408af5ea6c6ee9Vendor (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-azure5.14.21-150500.33.60.1 · 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-rt5.14.21-150500.13.61.1 · openSUSE:Leap 15.5Package registry (OSV)
opensuse:kernel-rt_debug5.14.21-150500.13.61.1 · openSUSE:Leap 15.5Package registry (OSV)
opensuse:kernel-source-azure5.14.21-150500.33.60.1 · openSUSE:Leap 15.5Package registry (OSV)
opensuse:kernel-source-rt5.14.21-150500.13.61.1 · openSUSE:Leap 15.5Package registry (OSV)
opensuse:kernel-syms-azure5.14.21-150500.33.60.1 · openSUSE:Leap 15.5Package registry (OSV)
opensuse:kernel-syms-rt5.14.21-150500.13.61.1 · openSUSE:Leap 15.5Package registry (OSV)
red hat:bpftool-debuginfo0:7.2.0-362.8.1.el9_3 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:kernel-64k-debug-debuginfo0:5.14.0-362.8.1.el9_3 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:kernel-64k-debug-devel0:5.14.0-362.8.1.el9_3 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:kernel-64k-debug-devel-matched0:5.14.0-362.8.1.el9_3 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:kernel-64k-debuginfo0:5.14.0-362.8.1.el9_3 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:kernel-64k-devel0:5.14.0-362.8.1.el9_3 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:kernel-64k-devel-matched0:5.14.0-362.8.1.el9_3 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:kernel-debug-debuginfo0:5.14.0-362.8.1.el9_3 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)

+16

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-476 · NULL Pointer Dereference

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 (5 more)

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

All records