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Progress Telerik UI for ASP.NET AJAX Deserialization of Untrusted Data Vulnerability

Known exploitedExploited · KEV 2021-11-03RansomwareMetasploit moduleCVE-2019-18935CWE-502

Exploited since 2021-11-03. 1 of 8 rule sources name it.

Edge rules
1/8
Our test
No exploit yet
CVSS
9.8
EPSS
99.7% Top 0.1%
Posts, 14d
02026-10-22: 0 posts2026-10-23: 0 posts2026-10-24: 0 posts2026-10-25: 0 posts2026-10-26: 0 posts2026-10-27: 0 posts2026-10-28: 0 posts2026-10-29: 0 posts2026-10-30: 0 posts2026-10-31: 0 posts2026-11-01: 0 posts2026-11-02: 0 posts2026-11-03: 0 posts2026-11-04: 0 posts
Published
2019-12-11
Progress Telerik UI for ASP.NET AJAX through 2019.3.1023 contains a .NET deserialization vulnerability in the RadAsyncUpload function. This is exploitable when the encryption keys are known due to the presence of CVE-2017-11317 or… More

Progress Telerik UI for ASP.NET AJAX through 2019.3.1023 contains a .NET deserialization vulnerability in the RadAsyncUpload function. This is exploitable when the encryption keys are known due to the presence of CVE-2017-11317 or CVE-2017-11357, or other means. Exploitation can result in remote code execution. (As of 2020.1.114, a default setting prevents the exploit. In 2019.3.1023, but not earlier versions, a non-default setting can prevent exploitation.)

Known exploitedLast checked 2026-11-04

The risk

CISA lists CVE-2019-18935 as exploited in the wild since 2021-11-03, including known use in ransomware campaigns. It is reachable over the network without credentials or any user interaction (CVSS 9.8). A Metasploit module exists, so exploitation needs no custom work.

Who is affected

Teams running Progress Telerik UI for ASP.NET AJAX. Affected versions are in the vendor advisory. Prioritise internet-facing instances.

Next steps

  1. Apply the vendor's fix; the advisory lists the affected and fixed versions.
  2. CISA's required action: Apply updates per vendor instructions. US federal agencies must act by 2022-05-03.
  3. Review exposed instances for signs of compromise: it was exploited before many systems were patched, and a later patch does not undo access already gained.
  4. Keep a WAF rule in place while you patch: Microsoft Azure ships a rule you may need to switch on. A WAF rule reduces exposure; it does not replace the patch. Edge coverage
  5. Check which WAF sits in front of your site and whether it covers this CVE. Check your domain

Exploitation activity

Last 90 days
Honeypot days
0 / 90
Last attempt seen
—
Listed exploited
—
Telegram claims
2 days, unverified

Attack traffic on Cloudflare

Cloudflare Radar
  • Remote Code Execution1.8% of mitigated layer 7 attacks, 7 days2026-10-06: 5.7%2026-10-07: 3.8%2026-10-08: 10.6%2026-10-09: 6.9%2026-10-10: 11.8%2026-10-11: 4.7%2026-10-12: 2.4%2026-10-13: 1.9%2026-10-14: 1.3%2026-10-15: 1.5%2026-10-16: 1.6%2026-10-17: 1.3%2026-10-18: 2.2%2026-10-19: 1.3%2026-10-20: 2.6%2026-10-21: 2.3%2026-10-22: 5.5%2026-10-23: 1.6%2026-10-24: 1.1%2026-10-25: 3.2%2026-10-26: 3.2%2026-10-27: 3%2026-10-28: 2.8%2026-10-29: 2.2%2026-10-30: 1.8%2026-10-31: 1.6%2026-11-01: 1.3%2026-11-02: 1.3%2026-11-03: 1.4%
  • Rules for named CVEs5.9% of mitigated layer 7 attacks, 7 days2026-10-06: 0.6%2026-10-07: 1.8%2026-10-08: 3%2026-10-09: 6.3%2026-10-10: 1.9%2026-10-11: 0.8%2026-10-12: 0.6%2026-10-13: 0.6%2026-10-14: 4.2%2026-10-15: 2.3%2026-10-16: 1.3%2026-10-17: 1.6%2026-10-18: 1.1%2026-10-19: 3.2%2026-10-20: 4.7%2026-10-21: 5.7%2026-10-22: 5.5%2026-10-23: 9.8%2026-10-24: 7%2026-10-25: 5%2026-10-26: 7.3%2026-10-27: 8.1%2026-10-28: 10.1%2026-10-29: 0.9%2026-10-30: 4.1%2026-10-31: 7.5%2026-11-01: 8.7%2026-11-02: 2.4%2026-11-03: 9.1%

Radar groups Cloudflare's WAF managed rules by category; it does not publish counts per CVE. These shares show how much attack traffic targets this kind of flaw across Cloudflare's network (28-day trend). They are not compromised systems, and seeing few attempts on Cloudflare does not prove an absence elsewhere. Radar data as of 2026-11-03. Radar ↗

Check your exposure with an agent

Read-only

Copy this into an agent with access to your infrastructure. It asks for an evidence-based, read-only assessment: affected systems, exposure, compensating controls and what is still unknown. It does not scan or change anything by itself.

Prompt12 lines
Assess whether the infrastructure available to you is affected by CVE-2019-18935 (Progress Telerik UI for ASP.NET AJAX Deserialization of Untrusted Data Vulnerability). Perform a read-only assessment within your authorized access. Do not send exploit traffic, scan third-party systems, change configuration or restart services.

1. Verify the CVE record at https://www.cve.org/CVERecord?id=CVE-2019-18935 and the vendor advisory. Establish affected and fixed versions, including vendor backports. Cite sources and retrieval dates; flag anything you cannot verify.
2. Inventory deployments of Progress Telerik UI for ASP.NET AJAX: asset, environment, owner where known, installed version or build, and how you confirmed it (package metadata, a version endpoint, image tags). An image tag alone does not prove the running version.
3. Identify which deployments are reachable from the internet or untrusted networks, and through which paths (direct origin, load balancer, CDN or WAF).
4. Assess compensating controls separately from patch status. Current edge WAF coverage for this CVE: Microsoft Azure: rule exists, check whether it is enabled. Live data: https://cve.vigilbase.com/api/v1/cves/CVE-2019-18935. Check whether the rule is enabled and in block mode on each path, and whether any path bypasses the WAF. A WAF rule is not a patch.
5. It is known exploited (CISA KEV): review logs on exposed instances for signs of exploitation before and after patching.

Return a short summary and a table: asset | version/build | assessment (affected, fixed, not applicable, unknown) | exposure | compensating control | evidence | next action. List what you could not assess and the access needed to resolve it. Do not infer absence of compromise from patch status or a lack of alerts.

Remediation guidance: Apply the vendor's fix; the advisory lists the affected and fixed versions. CISA's required action: Apply updates per vendor instructions. US federal agencies must act by 2022-05-03.
More: https://cve.vigilbase.com/cve/CVE-2019-18935

Sources

Cited
CVE record

CVSS 3.1 9.8 (critical). Weakness: CWE-502.

CVE-2019-18935 ↗NVD ↗

Exploit evidence

Metasploit has a module. Exploit-DB lists 1 exploit.

Metasploit: Telerik UI ASP.NET AJAX RadAsyncUpload Deserialization ↗Exploit-DB: Telerik UI - Remote Code Execution via Insecure Deserialization ↗

Seen exploited

Claimed in 2 Telegram posts (unverified).

CISA KEV

Added 2021-11-03, federal due date 2022-05-03, known ransomware use (catalog 2026.11.03, checked 2026-11-04).

CISA KEV catalog ↗

EPSS

99.7% probability of exploitation activity in the next 30 days, higher than 99% of CVEs (2026-11-02).

FIRST EPSS ↗

WAF vendor statements

Microsoft Azure names it in a changelog. Quotes and dates below.

Vendor statements

Ask Vigil

AI · answers from this page
Ask about CVE-2019-18935: who's covered, what to patch first, how vendors compare. I cite sources and won't help with attacks.

Severity, decoded

CVSS 3.1
Critical · 9.8 / 10

Exploitable over the network, with no privileges and no user interaction, leading to full loss of confidentiality, integrity and availability.

Over the internetNo login neededNo user actionWorks reliablyFull compromise
How the score is built8 metrics
  • Attack vectorAn attacker can reach it over the internet; no access to your network needed.
    Network
  • Attack complexityNo special conditions are needed; the attack works reliably.
    Low
  • Privileges requiredNo account or login is needed.
    None
  • User interactionNo one has to click or open anything; the attack works on its own.
    None
  • ScopeThe damage stays within the vulnerable component.
    Unchanged
  • Confidentiality impactAn attacker can read all data the affected component holds, or the most sensitive parts of it.
    High
  • Integrity impactAn attacker can change any data or files the affected component protects.
    High
  • Availability impactAn attacker can take the component down completely or keep it from serving anyone.
    High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CISA's assessmentSSVC, from the CVE record
ExploitationActive

Attackers are exploiting this in the wild.

AutomatableYes

Attackers can script the attack end to end and hit many targets at once.

Technical impactTotal

A successful attack gives full control over the affected software or all of its data.

Public exploits

2 found
1 Metasploit1 Exploit-DB0 Scanner template0 GitHub PoCs

Links are to third-party code: never run it outside an isolated lab.

Timeline

  1. 2019-12-09
    Metasploit module published
    Telerik UI ASP.NET AJAX RadAsyncUpload Deserialization
  2. 2019-12-11
    CVE published
    CVE List
  3. 2019-12-18
    Exploit published on Exploit-DB
    Telerik UI - Remote Code Execution via Insecure Deserialization
  4. 2021-11-03
    Added to CISA KEV
    Confirmed exploitation in the wild

Social

2026-10-22: 0 posts2026-10-23: 0 posts2026-10-24: 0 posts2026-10-25: 0 posts2026-10-26: 0 posts2026-10-27: 0 posts2026-10-28: 0 posts2026-10-29: 0 posts2026-10-30: 0 posts2026-10-31: 0 posts2026-11-01: 0 posts2026-11-02: 0 posts2026-11-03: 0 posts2026-11-04: 0 posts

No posts seen yet on X, Bluesky, Mastodon, Hacker News or GitHub.

Vendor statements

Quoted
CloudflareWAF Managed RulesBefore feed history

The CVE predates the oldest entry in this vendor's public feed, so a rule may exist that we cannot see.

AWSAWS WAF Managed RulesNo public claim

We found no public statement from this vendor naming this CVE. That is not proof of no protection: generic rules may still catch it. AWS often describes a vulnerability without naming its CVE (for example "Log4j"). We count only entries that name the CVE, so AWS coverage is understated.

Microsoft AzureFront Door and Application Gateway WAF (DRS)1 quoteRule published
UndatedListed99001012Source
Rule 99001012: Critical - 5 · 2 · Attempted Telerik WebUI insecure deserialization exploitation CVE-2019-18935
Google CloudCloud Armor preconfigured WAF rulesBefore feed history

The CVE predates the oldest entry in this vendor's public feed, so a rule may exist that we cannot see.

FastlyNext-Gen WAF virtual patchesBefore feed history

The CVE predates the oldest entry in this vendor's public feed, so a rule may exist that we cannot see.

F5Attack signatures (Distributed Cloud WAF)Before feed history

The CVE predates the oldest entry in this vendor's public feed, so a rule may exist that we cannot see.

AkamaiApp & API Protector (Adaptive Security Engine)No public source

This vendor publishes no machine-readable rule changelog we can check.

OWASP CRSCore Rule Set (open source, used inside many WAFs)Before feed history

The CVE predates the oldest entry in this vendor's public feed, so a rule may exist that we cannot see.