Traffic ServerApplication · Apache
CVE-2021-27577
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedIncorrect handling of url fragment vulnerability of Apache Traffic Server allows an attacker to poison the cache. This issue affects Apache Traffic Server 7.0.0 to 7.1.12, 8.0.0 to 8.1.1, 9.0.0 to 9.0.1.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · moderate confidenceApache Traffic Server improperly handles URL fragments (the portion after #) when processing requests, allowing attackers to poison the cache. By requesting the same resource with different fragments, an attacker can cause the server to cache distinct responses, potentially serving malicious content to subsequent users requesting the same base URL.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data
Traffic ServerApplication
>= 7.0.0, <= 7.1.12>= 8.0.0, <= 8.1.1>= 9.0.0, <= 9.0.1
Debian LinuxOperating system
= 8.0CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- High
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify if Apache Traffic Server is installedRun 'traffic_server -v' or check for the 'traffic_server' process with 'ps aux | grep traffic_server'. Also check for packages with 'dpkg -l | grep traffic-server' (Debian) or 'rpm -qa | grep traffic' (RPM-based).Affected if Apache Traffic Server is found running on the system
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Determine the installed versionExecute 'traffic_server -v' to get the version number, or check the package version installed via package manager.Affected if Version is 7.0.0-7.1.12, 8.0.0-8.1.1, or 9.0.0-9.0.1, or the system is Debian 8.0 with Apache Traffic Server installed
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Verify if caching is enabled in the configurationExamine the records.config file (typically in /etc/trafficserver/ or /usr/local/etc/trafficserver/) and look for the 'proxy.config.http.cache.enabled' setting, or use 'traffic_ctl config get proxy.config.http.cache.enabled'.Affected if Caching is enabled (value set to 1 or enabled)
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Check if the ATS instance is exposed to untrusted upstream clientsReview the proxy.config.http.cache.urls_that_match_hex_prefix configuration and network exposure settings to determine if the cache can be reached by external or untrusted users.Affected if The cache is accessible to untrusted clients or upstream users who can send arbitrary requests
A user is affected if Apache Traffic Server is running with a vulnerable version AND caching is enabled AND the server accepts requests from untrusted sources, allowing them to exploit URL fragment handling to poison the cache.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor dataUpgrade Apache Traffic Server to a patched version beyond 9.0.1. If immediate patching is not possible, consider disabling caching for sensitive resources or implementing WAF rules to normalize/remove URL fragments from incoming requests.
Fix this in Traffic Server
Scoped from the published advisory
- Consultation2.0 h
- Implementation4.0 h
- Testing6.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,808.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-27577 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2021-27577 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Version or environment caveats, and links to real fixes
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