FedoraOperating system · Fedoraproject
CVE-2021-43818
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 · uneditedlxml is a library for processing XML and HTML in the Python language. Prior to version 4.6.5, the HTML Cleaner in lxml.html lets certain crafted script content pass through, as well as script content in SVG files embedded using data URIs. Users that employ the HTML cleaner in a security relevant context should upgrade to lxml 4.6.5 to receive a patch. There are no known workarounds available.
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 analysisUntrusted input crosses into a downstream interpreter — SQL, a shell, an HTML page, an LDAP query — without being kept separate from the commands around it, so the attacker's data is read as instructions. This is the parent class behind SQL injection, cross-site scripting, and command injection alike. The durable fix is the same everywhere: keep data and code apart at every boundary, using parameterisation or context-aware encoding rather than building interpreted strings by concatenation.
General guidance for the injection class — the official description and references above are authoritative for this specific CVE. Want a bespoke review and a reviewed fix? Ask our team →
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
FedoraOperating system
= 34= 35
Debian LinuxOperating system
= 9.0= 10.0= 11.0
HTTP ServerWeb server / proxy
= 12.2.1.3.0= 12.2.1.4.0< 4.6.5all versionsall versionsall versions= 22.1.3CVSS 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
- Required
- Scope
- Changed
- Confidentiality
- Low
- Integrity
- Low
- Availability
- Low
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:L
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.
dbcve · scoped4.6.5
lxml 4.6.5
- 1. Identify the Python environment where lxml is installed (e.g., virtual environment, system Python, container)
- 2. Run 'pip show lxml' to confirm the currently installed version
- 3. Run 'pip install lxml==4.6.5' to upgrade to the fixed version
- 4. Alternatively, run 'pip install lxml>=4.6.5' to get the latest stable version with the fix
- 5. Verify the upgrade was successful by running 'pip show lxml' and confirming the version number
- 6. Run any existing tests to ensure the upgrade does not break functionality
- 7. Rebuild and redeploy any applications or containers that depend on the updated lxml package
Generated from the published advisory — verify against the referenced sources before acting.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-43818 — 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-2021-43818 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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