NVD / CVE Program· CNA Linux

CVE-2021-47010: net: Only allow init netns to set default tcp cong to a restricted algo

Noroxi assessment

Priority: Monitor (action score 31/100)

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: 0.25% (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 6c1ea8bee75df8fe2184a50fcd0f70bf82986f42, 8d432592f30fcc34ef5a10aac4887b4897884493, 9884f745108f7d25b189bbcd6754e284fb29ab68.
Mentioned 1 time in Turkish national cyber security advisories (siberguvenlik.gov.tr).

Low priority for now. Upgrade to Linux Linux 6c1ea8bee75df8fe2184a50fcd0f70bf82986f42, 8d432592f30fcc34ef5a10aac4887b4897884493, 9884f745108f7d25b189bbcd6754e284fb29ab68 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: net: Only allow init netns to set default tcp cong to a restricted algo tcp_set_default_congestion_control() is netns-safe in that it writes to &net->ipv4.tcp_congestion_control, but it also sets ca->flags |= TCP_CONG_NON_RESTRICTED which is not namespaced. This has the unintended side-effect of changing the global net.ipv4.tcp_allowed_congestion_control sysctl, despite the fact that it is read-only: 97684f0970f6 ("net: Make tcp_allowed_congestion_control readonly in non-init netns") Resolve this netns "leak" by only allowing the init netns to set the default algorithm to one that is restricted. This restriction could be removed if tcp_allowed_congestion_control were namespace-ified in the future. This bug was uncovered with https://github.com/JonathonReinhart/linux-netns-sysctl-verify

HighCVSS 7.8 · v3.1—No exploit Fix available

Denial of service

BDU:2025-00809

Published: Feb 28, 2024
Updated: Jun 17, 2026
EPSS: 0.2% · 17th percentile
CWE: CWE-400

Report tools

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Action score

Monitor

Low priority for now.

CVSS: 31 / 40 · 7.8 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 0.2%

CISA SSVC decision

Exploitation: none
Automatable: no
Technical impact: total

Vulnrichment: CISA's decision-tree inputs.

Get told when this record changes

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?

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.

Vendor	Product	CPE
linux	linux kernel	cpe:2.3:o:linux:linux_kernel

Affected versions

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

linux linux kernel4.15 and later · before 4.19.191
linux linux kernel4.20 and later · before 5.4.119
linux linux kernel5.5 and later · before 5.10.37
linux linux kernel5.11 and later · before 5.11.21
linux linux kernel5.12 and later · before 5.12.4

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
- 4.15affected
- 6670e152447732ba90626f36dfc015a13fbf150e and later · before 992de06308d9a9584d59b96d294ac676f924e437affected · git
- 6670e152447732ba90626f36dfc015a13fbf150e and later · before 9884f745108f7d25b189bbcd6754e284fb29ab68affected · git
- 6670e152447732ba90626f36dfc015a13fbf150e and later · before 6c1ea8bee75df8fe2184a50fcd0f70bf82986f42affected · git
- 6670e152447732ba90626f36dfc015a13fbf150e and later · before efe1532a6e1a8e3c343d04fff510f0ed80328f9caffected · git
- 6670e152447732ba90626f36dfc015a13fbf150e and later · before e7d7bedd507bb732e600403b7a96f9fe48d0ca31affected · git
- 6670e152447732ba90626f36dfc015a13fbf150e and later · before 8d432592f30fcc34ef5a10aac4887b4897884493affected · git
- before 4.15not affected · semver
- 4.19.191 and later · up to and including 4.19.*not affected · semver
- 5.4.119 and later · up to and including 5.4.*not affected · semver

Package-level exposure

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

Ecosystem	Package	Affected range	Fix
Debian:12	linux	before 5.10.38-1	5.10.38-1

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-2021-47008Feb 28, 2024 · KVM: SVM: Make sure GHCB is mapped before updating
22Monitor
← EarlierCVE-2021-47009Feb 28, 2024 · KEYS: trusted: Fix memory leak on object td
22Monitor
Later →CVE-2021-47011Feb 28, 2024 · mm: memcontrol: slab: fix obtain a reference to a freeing memcg
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 / package	Fixed version	Source
Linux Linux	6c1ea8bee75df8fe2184a50fcd0f70bf82986f42	Vendor (CNA)
Linux Linux	8d432592f30fcc34ef5a10aac4887b4897884493	Vendor (CNA)
Linux Linux	9884f745108f7d25b189bbcd6754e284fb29ab68	Vendor (CNA)
Linux Linux	992de06308d9a9584d59b96d294ac676f924e437	Vendor (CNA)
Linux Linux	e7d7bedd507bb732e600403b7a96f9fe48d0ca31	Vendor (CNA)
Linux Linux	efe1532a6e1a8e3c343d04fff510f0ed80328f9c	Vendor (CNA)
debian:linux	5.10.38-1 · Debian:12	Package registry (OSV)

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.

CVE-2024-39462118 days apartclk: bcm: dvp: Assign ->num before accessing ->hws
39Monitor
CVE-2021-4440118 days apartx86/xen: Drop USERGS_SYSRET64 paravirt call
35Monitor
CVE-2021-4731383 days apartcpufreq: CPPC: Fix potential memleak in cppc_cpufreq_cpu_init
33Monitor
CVE-2021-470230 days apartnet: marvell: prestera: fix port event handling on init
32Monitor
CVE-2024-38616112 days apartwifi: carl9170: re-fix fortified-memset warning
32Monitor
CVE-2023-526027 days apartjfs: fix slab-out-of-bounds Read in dtSearch
31Monitor

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.

TR-24-0145 · Feb 29, 2024(Linux Kernel Güncellemesi)

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: high · data can be read
Integrity: high · data or configuration can be modified
Availability: high · the service can be disrupted

Attack vector: Local
Attack complexity: Low
Privileges required: Low
User interaction: None
Scope: Unchanged
Confidentiality impact: High
Integrity impact: High
Availability impact: High

Weakness class (CWE)

CWE-400 · Uncontrolled Resource Consumption

CVSS vector

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

nvd-secondary

Root cause

Code that parses nested structures sets no depth or size limit. A small input can turn into a disproportionate processing load.

The bug in code

The whole CWE-400 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

1function expand(node) {
2  return node.children.map(expand);
3}

Fixed

1const MAX_DEPTH = 32;
2function expand(node, depth = 0) {
3  if (depth > MAX_DEPTH) throw new Error("too deep");
4  return node.children.map((c) => expand(c, depth + 1));
5}

Attack context

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

Attack patterns (CAPEC)

ATT&CK techniques

Endpoint Denial of ServiceT1499

Change log

Fix✗ → ✓Sep 28, 2026, 10:09 PM UTC

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

References

git.kernel.org/stable/c/6c1ea8bee75df8fe2184a50fcd0f70bf82986f42

Show all references (5 more)

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

All records