Security readout for executives and security teams
Plain-English summary
An older Telerik UI for ASP.NET AJAX upload component can let unauthenticated attackers run code on the server if required encryption keys are known or recoverable. CISA lists it as known exploited, and public reporting describes data theft at a US federal agency. Internet-facing legacy ASP.NET apps should be treated as urgent.
Executive priority
Treat this as an immediate remediation item for any internet-facing legacy Telerik deployment. The vulnerability is critical, known exploited, and can lead to full server compromise when prerequisites are met.
Technical view
CVE-2019-18935 is CWE-502 .NET deserialization in RadAsyncUpload through 2019.3.1023. Exploitation requires known Telerik encryption keys, often via CVE-2017-11317, CVE-2017-11357, or other exposure. The CVSS 3.1 score is 9.8 and successful exploitation can produce remote code execution.
Likely exposure
Exposure is most likely in legacy ASP.NET applications using Telerik UI for ASP.NET AJAX through 2019.3.1023, especially internet-facing apps with RadAsyncUpload reachable and Telerik encryption keys exposed or guessable.
Exploitation context
Active exploitation is supported by CISA KEV listing and public reporting. Public research and exploit references exist, but the provided sources do not prove every deployment is exploitable without known encryption keys or vulnerable configuration.
Researcher notes
Key prerequisites matter: the flaw is exploitable when encryption keys are known through prior Telerik vulnerabilities or other means. Validate version, handler reachability, key exposure, and configuration before declaring exploitability. Avoid relying only on package inventory.
Mitigation direction
- Upgrade Telerik UI for ASP.NET AJAX per Progress guidance.
- Prioritize versions at or beyond 2020.1.114 where the default blocks this exploit path.
- Rotate Telerik encryption keys if compromise or exposure is possible.
- Review vendor KB guidance for secure RadAsyncUpload configuration.
- Restrict exposure of legacy ASP.NET applications until patched or validated.
- Investigate for compromise on internet-facing affected systems.
Validation and detection
- Inventory ASP.NET applications using Telerik UI for ASP.NET AJAX.
- Identify exact Telerik UI versions and flag versions through 2019.3.1023.
- Check whether RadAsyncUpload endpoints are reachable externally.
- Verify Telerik encryption keys are not exposed or reused from older vulnerable states.
- Review logs for suspicious upload handler activity and post-exploitation indicators.
- Confirm deployed configuration matches Progress mitigation guidance.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-502: Code execution behavior lookup
Code execution and unsafe deserialization weaknesses often justify reviewing execution behavior and process telemetry. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupExecution behavior lookup
The CVE wording references code or command execution, so execution technique review may help defensive triage. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2019-18935 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Critical
- CVSS
- 9.8 (3.1)
- Known Exploited
- Yes
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CISA KEV status
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H3.95.9Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
9.8CriticalVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://www.telerik.com/support/whats-new/release-historyCVE reference
- https://codewhitesec.blogspot.com/2019/02/telerik-revisited.htmlCVE reference
- https://www.telerik.com/support/kb/aspnet-ajax/details/allows-javascriptserializer-deserializationCVE reference
- https://github.com/bao7uo/RAU_cryptoCVE reference
- https://know.bishopfox.com/research/cve-2019-18935-remote-code-execution-in-telerik-uiCVE reference
- https://github.com/noperator/CVE-2019-18935CVE reference
- https://www.telerik.com/support/whats-new/aspnet-ajax/release-history/ui-for-asp-net-ajax-r1-2020-%28version-2020-1-114%29CVE reference
- https://www.bleepingcomputer.com/news/security/us-federal-agency-hacked-using-old-telerik-bug-to-steal-data/CVE reference
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2019-18935CVE reference · government-resource
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Deserialization of Untrusted Data
Deserialization of Untrusted Data represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.