FedoraOperating system · Fedoraproject
CVE-2021-34551
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 · uneditedPHPMailer before 6.5.0 on Windows allows remote code execution if lang_path is untrusted data and has a UNC pathname.
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 · high confidencePHPMailer before 6.5.0 on Windows allows remote code execution when the lang_path parameter accepts untrusted user input containing a UNC pathname (e.g., \\attacker\share). An attacker who controls the lang_path value can inject malicious paths that lead to code execution, specifically on Windows environments where UNC paths are interpreted.
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
FedoraOperating system
= 33= 34< 6.5.0CVSS 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
- High
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
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 PHPMailer installation and versionLocate the PHPMailer library in your project (commonly in vendor folder via Composer, or included directly). Check the version number in the main class file or composer.jsonAffected if The installed version is lower than 6.5.0 and the application runs on Windows
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Determine the operating system environmentCheck if the server or application runs on Windows OS. This can be done via PHP's PHP_OS constant, php_uname('s'), or system configurationAffected if The environment is Windows - UNC path injection only works on Windows systems
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Locate code that sets the lang_path parameterSearch your codebase for instances where lang_path is being set, particularly in PHPMailer initialization calls. Look for patterns like $mail->setLanguage() or direct property assignment to $mail->LangPathAffected if The lang_path parameter is being set or configured in the code
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Inspect whether lang_path accepts external inputReview how lang_path is configured - check if it directly or indirectly accepts user-supplied input, query parameters, or configuration from untrusted sources. Look for variable interpolation in the lang_path valueAffected if The lang_path value is derived from user input, request parameters, or other untrusted sources rather than being hardcoded to a safe filesystem path
You are affected if PHPMailer version is below 6.5.0, the application runs on Windows, and the lang_path parameter accepts untrusted user-controlled input containing UNC paths.
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 data6.5.0
Update PHPMailer to version 6.5.0 or later. Additionally, validate and sanitize the lang_path parameter to ensure it does not accept untrusted input, particularly UNC paths, and restrict it to trusted filesystem paths only.
Fix this in Fedora
Scoped from the published advisory
- Consultation2.0 h
- Implementation2.0 h
- Testing3.0 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 $2,224.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-34551 — 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-2021-34551 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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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
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