CVE-2021-47304

Kernel memory exhaustion via congestion-control double initialization

Published May 21, 2024 · Updated May 11, 2026

Memory leak in the Linux kernel TCP stack allows local users to exhaust kernel memory through congestion-control changes. tcp_init_transfer resets icsk_ca_initialized after setsockopt(TCP_CONGESTION) has initialized the selected module, causing another init callback without an intervening release. Reachability requires a Fast Open socket in TCP_SYN_SENT; allocating modules such as CDG then leak each repeated initialization allocation.

CVSS severity5.5
Medium
EPSS probability0.24%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Memory leak in the Linux kernel TCP stack allows local users to exhaust kernel memory through congestion-control changes. tcp_init_transfer resets icsk_ca_initialized after setsockopt(TCP_CONGESTION) has initialized the selected module, causing another init callback without an intervening release. Reachability requires a Fast Open socket in TCP_SYN_SENT; allocating modules such as CDG then leak each repeated initialization allocation.

The record

CVE
CVE-2021-47304
Published
May 21, 2024
Updated
May 11, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-415, T1499
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. May 21, 2024CVE publishedPublication date reported by the CVE source.
  2. May 11, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=5.10
  2. Affected versionversion=8919a9b31eb4fb4c0a93e5fb350a626924302aa6 <ad4ba3404931745a5977ad12db4f0c34080e52f7
  3. Affected versionversion=8919a9b31eb4fb4c0a93e5fb350a626924302aa6 <be5d1b61a2ad28c7e57fe8bfa277373e8ecffcdc
  4. Affected versionversion=8919a9b31eb4fb4c0a93e5fb350a626924302aa6 <fe77b85828ca9ddc42977b79de9e40d18545b4fe

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=5.10; version=8919a9b31eb4fb4c0a93e5fb350a626924302aa6 <ad4ba3404931745a5977ad12db4f0c34080e52f7; version=8919a9b31eb4fb4c0a93e5fb350a626924302aa6 <be5d1b61a2ad28c7e57fe8bfa277373e8ecffcdc; version=8919a9b31eb4fb4c0a93e5fb350a626924302aa6 <fe77b85828ca9ddc42977b79de9e40d18545b4fe

Published CVSS scores

5.5NIST National Vulnerability DatabaseCVSS: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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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

CWE-415Double Free
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo