RexmlApplication · Ruby Lang
CVE-2021-28965
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 · uneditedThe REXML gem before 3.2.5 in Ruby before 2.6.7, 2.7.x before 2.7.3, and 3.x before 3.0.1 does not properly address XML round-trip issues. An incorrect document can be produced after parsing and serializing.
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 confidenceThe REXML gem in Ruby versions before 2.6.7, 2.7.3, and 3.0.1 contains a round-trip vulnerability where parsing an XML document and serializing it back produces an incorrect output. This can lead to security issues such as XML signature wrapping or unexpected behavior when applications rely on XML round-tripping for validation or processing.
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
RexmlApplication
< 3.2.5
RubyApplication
< 2.6.7>= 2.7.0, < 2.7.3>= 3.0.0, < 3.0.1
FedoraOperating system
= 34CVSS 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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Check installed Ruby versionRun `ruby --version` or `ruby -v` to display the installed Ruby interpreter version.Affected if The version is less than 2.6.7, or between 2.7.0 and 2.7.3 exclusive, or between 3.0.0 and 3.0.1 exclusive
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Check REXML gem versionRun `gem list rexml` or open Ruby and run `require 'rexml'; puts REXML::VERSION` to display the installed REXML gem version.Affected if The REXML version is less than 3.2.5
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Identify XML round-trip usageReview application code for patterns that parse XML documents and serialize them back, such as REXML::Document.new followed by .to_s or .write, or any XML validation workflows that rely on re-serialization.Affected if The application parses XML and serializes it back to string or file
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Check Fedora version (if applicable)Run `cat /etc/fedora-release` or `fedora-release` to identify the Fedora version.Affected if Running Fedora 34 with an affected Ruby or REXML version
You are affected if your Ruby version or REXML gem version falls within the vulnerable ranges AND your application performs XML round-trip parsing and serialization.
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 data2.6.72.7.33.0.1
Update Ruby to version 2.6.7+, 2.7.3+, 3.0.1+ or later, or update the REXML gem to version 3.2.5 or later to address the round-trip vulnerability.
Fix this in Rexml
Scoped from the published advisory
- Consultation1.0 h
- Implementation2.0 h
- Testing2.0 h
- Review / QA1.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,664.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-28965 — 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-2021-28965 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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