CVE-2021-47295

Service interruption via leaked tcindex perfect hashes

Published May 21, 2024 · Updated May 11, 2026

Resource exhaustion in Linux kernel 3.18 through 5.14-rc2 allows local users to deplete memory through crafted tcindex updates. tcindex_set_parms replaces its tcindex_data object without transferring the perfect-hash allocation, while tcindex_partial_destroy_work fails to free that orphaned allocation. Local access with traffic-control privileges is required; repeated classifier replacement can eventually interrupt host services.

CVSS severity7.5
High
EPSS probability1.50%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Resource exhaustion in Linux kernel 3.18 through 5.14-rc2 allows local users to deplete memory through crafted tcindex updates. tcindex_set_parms replaces its tcindex_data object without transferring the perfect-hash allocation, while tcindex_partial_destroy_work fails to free that orphaned allocation. Local access with traffic-control privileges is required; repeated classifier replacement can eventually interrupt host services.

The record

CVE
CVE-2021-47295
Published
May 21, 2024
Updated
May 11, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-401, T1499.004
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

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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=3.18
  2. Affected versionversion=331b72922c5f58d48fd5500acadc91777cc31970 <01d0d2b8b4e3cf2110baba9371c0c3d04ad5c77b
  3. Affected versionversion=331b72922c5f58d48fd5500acadc91777cc31970 <18c3fa7a7fdbb4d21dafc8a7710ae2c1680930f6
  4. Affected versionversion=331b72922c5f58d48fd5500acadc91777cc31970 <372ae77cf11d11fb118cbe2d37def9dd5f826abd
  5. Affected versionversion=331b72922c5f58d48fd5500acadc91777cc31970 <3abebc503a5148072052c229c6b04b329a420ecd
  6. Affected versionversion=331b72922c5f58d48fd5500acadc91777cc31970 <53af9c793f644d5841d84d8e0ad83bd7ab47f3e0
  7. Affected versionversion=331b72922c5f58d48fd5500acadc91777cc31970 <7a6fb69bbcb21e9ce13bdf18c008c268874f0480
  8. Affected versionversion=331b72922c5f58d48fd5500acadc91777cc31970 <7c183dc0af472dec33d2c0786a5e356baa8cad19
  9. Affected versionversion=331b72922c5f58d48fd5500acadc91777cc31970 <8d7924ce85bae64e7a67c366c7c50840f49f3a62
  10. Affected versionversion=331b72922c5f58d48fd5500acadc91777cc31970 <8e9662fde6d63c78eb1350f6167f64c9d71a865b
  11. Affected versionversion=331b72922c5f58d48fd5500acadc91777cc31970 <cac71d27745f92ee13f0ecc668ffe151a4a9c9b1
  12. Affected versionversion=331b72922c5f58d48fd5500acadc91777cc31970 <f5051bcece50140abd1a11a2d36dc3ec5484fc32

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=3.18; version=331b72922c5f58d48fd5500acadc91777cc31970 <01d0d2b8b4e3cf2110baba9371c0c3d04ad5c77b; version=331b72922c5f58d48fd5500acadc91777cc31970 <18c3fa7a7fdbb4d21dafc8a7710ae2c1680930f6; version=331b72922c5f58d48fd5500acadc91777cc31970 <372ae77cf11d11fb118cbe2d37def9dd5f826abd; version=331b72922c5f58d48fd5500acadc91777cc31970 <3abebc503a5148072052c229c6b04b329a420ecd; version=331b72922c5f58d48fd5500acadc91777cc31970 <53af9c793f644d5841d84d8e0ad83bd7ab47f3e0; version=331b72922c5f58d48fd5500acadc91777cc31970 <7a6fb69bbcb21e9ce13bdf18c008c268874f0480; version=331b72922c5f58d48fd5500acadc91777cc31970 <7c183dc0af472dec33d2c0786a5e356baa8cad19; version=331b72922c5f58d48fd5500acadc91777cc31970 <8d7924ce85bae64e7a67c366c7c50840f49f3a62; version=331b72922c5f58d48fd5500acadc91777cc31970 <8e9662fde6d63c78eb1350f6167f64c9d71a865b; version=331b72922c5f58d48fd5500acadc91777cc31970 <cac71d27745f92ee13f0ecc668ffe151a4a9c9b1; version=331b72922c5f58d48fd5500acadc91777cc31970 <f5051bcece50140abd1a11a2d36dc3ec5484fc32
The Linux Kernel Organization · Linux Kernelversion=3.18; version=331b72922c5f <8d7924ce85ba; version=331b72922c5f <8e9662fde6d6; version=331b72922c5f <cac71d27745f; version=331b72922c5f <f5051bcece50

Published CVSS scores

5.5Amazon LinuxCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
7.5NVDCVSS:3.1/AV:N/AC:L/PR:N/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

CWE-401Missing Release of Memory after Effective Lifetime
T1499.004Application or System Exploitation

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

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Your stack

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