CVE-2026-2878
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 · uneditedIn Progress® Telerik® UI for AJAX, versions prior to 2026.1.225, an insufficient entropy vulnerability exists in RadAsyncUpload, where a predictable temporary identifier, based on timestamp and filename, can enable collisions and file content tampering.
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 confidenceIn Progress Telerik UI for AJAX, the RadAsyncUpload component uses a predictable temporary file identifier generated from timestamp and filename, resulting in insufficient entropy. This allows attackers to predict identifiers, cause file collisions, and potentially tamper with uploaded file content.
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< 2026.1.225CVSS 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
- None
- Integrity
- High
- Availability
- None
CVSS:3.1/AV:N/AC:H/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 Telerik UI for AJAX installation and versionInspect the web.config file for the Telerik.Web.UI assembly version, or check the Telerik.Web.UI.dll file version in the bin folder, or review the installed NuGet package version.Affected if The installed version is lower than 2026.1.225
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Confirm RadAsyncUpload component is in useSearch the codebase for references to RadAsyncUpload in .aspx, .ascx, or code-behind files, and verify the Telerik.AsyncUpload handler is registered in web.config.Affected if RadAsyncUpload is actively used or configured in the application
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Check temporary file handler configurationExamine the web.config for Telerik.Web.UI.Upload handler settings and the Telerik.AsyncUpload handler configuration under system.webServer/handlers.Affected if The AsyncUpload handler is enabled and processing file uploads
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Verify temporary file naming behaviorUpload a test file via RadAsyncUpload and inspect the temporary file created in the configured upload folder (typically App_Data/RadUploadTemp).Affected if The temporary filename follows a predictable pattern based on timestamp and original filename rather than a cryptographically random identifier
The environment is affected if Telerik UI for AJAX version is below 2026.1.225 AND the RadAsyncUpload component is enabled and processing file uploads.
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.
dbcve · scoped2026.1.225
Upgrade to Telerik UI for AJAX version 2026.1.225 or later, which implements cryptographically secure random identifiers for temporary files.
2026.1.225
- Download Telerik UI for ASP.NET AJAX version 2026.1.225 or later from the official Telerik website (www.telerik.com)
- Back up your current application and project files
- Update the Telerik UI for ASP.NET AJAX package reference in your project to version 2026.1.225
- Rebuild and test the application, specifically testing RadAsyncUpload functionality to verify the vulnerability is resolved
- Deploy the updated application to production
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation2.0 h
- Implementation4.0 h
- Testing3.0 h
- Review / QA1.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-2878 — 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-2026-2878 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
- No spam, self-promotion, credentials, or personal data