CVE-2021-27577Network attack vector

Cache poisoning via forwarded URL fragments

Published Jun 29, 2021 · Updated Aug 3, 2024

URL-fragment handling in Apache Traffic Server affected releases allows remote attackers to poison shared cache entries via crafted requests. HttpTransact::build_request retained a client-supplied fragment when constructing the upstream request instead of removing the client-only component. An unauthenticated network request can therefore make the proxy cache origin content under a mismatched URL, compromising later responses served from that shared cache.

CVSS severity7.5
High
EPSS probability3.54%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

URL-fragment handling in Apache Traffic Server affected releases allows remote attackers to poison shared cache entries via crafted requests. HttpTransact::build_request retained a client-supplied fragment when constructing the upstream request instead of removing the client-only component. An unauthenticated network request can therefore make the proxy cache origin content under a mismatched URL, compromising later responses served from that shared cache.

The record

CVE
CVE-2021-27577
Published
Jun 29, 2021
Updated
Aug 3, 2024
Vendor
The Apache Software Foundation
Product
Apache Traffic Server
Classifications
CWE-444, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 29, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 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 NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
5.0NIST NVDAV:N/AC:L/Au:N/C:N/I:P/A:N

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)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-444Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
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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