CVE-2021-35474Network attack vector

Proxy crash via undersized percent-encoding buffer

Published Jun 30, 2021 · Updated Aug 4, 2024

Buffer overflow in Apache Traffic Server 7.0.0 through 7.1.12, 8.0.0 through 8.1.1, and 9.0.0 through 9.0.1 allows remote attackers to crash the proxy. The cachekey plugin's appendEncoded function allocates len2 stack bytes even though percent encoding can require len3 bytes plus a terminator. A crafted HTTP request must reach an enabled cachekey plugin; the resulting overwrite corrupts the proxy process stack and interrupts service.

CVSS severity9.8
Critical
EPSS probability2.71%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Buffer overflow in Apache Traffic Server 7.0.0 through 7.1.12, 8.0.0 through 8.1.1, and 9.0.0 through 9.0.1 allows remote attackers to crash the proxy. The cachekey plugin's appendEncoded function allocates len2 stack bytes even though percent encoding can require len3 bytes plus a terminator. A crafted HTTP request must reach an enabled cachekey plugin; the resulting overwrite corrupts the proxy process stack and interrupts service.

The record

CVE
CVE-2021-35474
Published
Jun 30, 2021
Updated
Aug 4, 2024
Vendor
The Apache Software Foundation
Product
Apache Traffic Server
Classifications
CWE-121, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 30, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record 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=Apache Traffic Server 7.0.0 to 7.1.12, 8.0.0 to 8.1.1, 9.0.0 to 9.0.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Apache Software Foundation · Apache Traffic Serverversion=Apache Traffic Server 7.0.0 to 7.1.12, 8.0.0 to 8.1.1, 9.0.0 to 9.0.1

Published CVSS scores

7.5NIST NVDAV:N/AC:L/Au:N/C:P/I:P/A:P
9.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-121Stack-based Buffer Overflow
T1190Exploit Public-Facing Application

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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