{"id":"CVE-2021-23758","published":"2021-12-03T20:15:07Z","modified":"2026-08-27T04:16:38Z","title":"Ajax.NET Professional Deserialization of Untrusted Data Vulnerability","vendor":"Ajax.NET Professional","product":"Ajax.NET Professional","tier":"core","eol":null,"description":{"text":"All versions of package ajaxpro.2 are vulnerable to Deserialization of Untrusted Data due to the possibility of deserialization of arbitrary .NET classes, which can be abused to gain remote code execution.","provenance":"source","from":"NVD"},"summary":{"text":"Ajax.NET Professional (the ajaxpro.2 package) contains a deserialization of untrusted data flaw, which permits deserialization of arbitrary .NET classes. An attacker with network access can exploit this without authentication or user interaction, using a crafted request to gain remote code execution.","provenance":"ai","model":"claude-haiku-5-5","generatedAt":"2026-10-23T07:09:50Z"},"cvss":{"score":9.8,"severity":"CRITICAL","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","provenance":"source","from":"NVD"},"epss":{"score":0.82578,"percentile":0.99664,"date":"2026-10-29","provenance":"source"},"kev":{"dateAdded":"2026-08-26","dueDate":"2026-09-09","ransomware":false,"requiredAction":"Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.","notes":"This vulnerability affects an open-source component, third-party library, protocol, or proprietary implementation that could be used by different products. For more information, please see: https://github.com/michaelschwarz/Ajax.NET-Professional/commit/b0e63be5f0bb20dfce507cb8a1a9568f6e73de57 ; BOD 26-04: https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk ; Forensics Triage Requirements: https://www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-based-risk ; https://nvd.nist.gov/vuln/detail/CVE-2021-23758","provenance":"source"},"vulncheckKev":{"dateAdded":"2026-08-20","exploitedFirstSeen":"2026-08-20","ransomware":false,"evidence":[{"url":"https://blog.talosintelligence.com/uat-10147-chinese-speaking-adversary-integrates-agentic-ai-into-post-compromise-operations/","date":"2026-08-20"},{"url":"https://previdian.com/CVE-2021-23758","date":"2026-08-26"},{"url":"https://www.cisa.gov/sites/default/files/feeds/known_exploited_vulnerabilities.json","date":"2026-08-26"},{"url":"https://www.recordedfuture.com/blog/august-2026-cve-landscape","date":"2026-09-08"}],"evidenceTotal":4,"provenance":"source"},"exploited":true,"otx":{"pulseCount":34,"pulses":[{"name":"Actively_Exploited_Kev | Oct 29, 2026","url":"https://otx.alienvault.com/pulse/6ae20c1db17e7057ae7d9ad1","created":"2026-10-28"},{"name":"Actively_Exploited_Kev | Oct 28, 2026","url":"https://otx.alienvault.com/pulse/6ae0ba7e0e2a97ff7b218819","created":"2026-10-27"},{"name":"Actively_Exploited_Kev | Oct 27, 2026","url":"https://otx.alienvault.com/pulse/6adf68b85c3e852f3c111d18","created":"2026-10-26"},{"name":"Actively_Exploited_Kev | Oct 24, 2026","url":"https://otx.alienvault.com/pulse/6adb740e397c3ad4799aa4cd","created":"2026-10-23"},{"name":"Actively_Exploited_Kev | Oct 23, 2026","url":"https://otx.alienvault.com/pulse/6ada236fcfba2dfa730ea482","created":"2026-10-22"},{"name":"Actively_Exploited_Kev | Oct 22, 2026","url":"https://otx.alienvault.com/pulse/6ad8d33a077cbb5cab524d80","created":"2026-10-21"},{"name":"Actively_Exploited_Kev | Oct 21, 2026","url":"https://otx.alienvault.com/pulse/6ad78130c4d1ac2be83a8b6d","created":"2026-10-20"},{"name":"Actively_Exploited_Kev | Oct 20, 2026","url":"https://otx.alienvault.com/pulse/6ad62f63c24a405a3423cc13","created":"2026-10-19"},{"name":"Actively_Exploited_Kev | Oct 19, 2026","url":"https://otx.alienvault.com/pulse/6ad4dda174e5797d0bd238b7","created":"2026-10-18"},{"name":"Actively_Exploited_Kev | Oct 18, 2026","url":"https://otx.alienvault.com/pulse/6ad38c22e1848f8189d1c121","created":"2026-10-17"}],"provenance":"machine"},"cwes":[{"id":"CWE-502","name":"Deserialization of Untrusted Data"}],"references":[{"url":"http://packetstormsecurity.com/files/175677/AjaxPro-Deserialization-Remote-Code-Execution.html","tags":["Exploit","VDB Entry"]},{"url":"https://github.com/michaelschwarz/Ajax.NET-Professional/commit/b0e63be5f0bb20dfce507cb8a1a9568f6e73de57","tags":["Patch","Third Party Advisory"]},{"url":"https://snyk.io/vuln/SNYK-DOTNET-AJAXPRO2-1925971","tags":["Third Party Advisory"]},{"url":"http://packetstormsecurity.com/files/175677/AjaxPro-Deserialization-Remote-Code-Execution.html","tags":["Exploit","VDB Entry"]},{"url":"https://github.com/michaelschwarz/Ajax.NET-Professional/commit/b0e63be5f0bb20dfce507cb8a1a9568f6e73de57","tags":["Patch","Third Party Advisory"]},{"url":"https://snyk.io/vuln/SNYK-DOTNET-AJAXPRO2-1925971","tags":["Third Party Advisory"]},{"url":"https://blog.talosintelligence.com/uat-10147-chinese-speaking-adversary-integrates-agentic-ai-into-post-compromise-operations/","tags":["Exploit","Third Party Advisory"]},{"url":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-23758","tags":["US Government Resource"]}],"techniques":[{"id":"T1190","name":"Exploit Public-Facing Application","tactics":["initial-access"],"provenance":"ai","basis":"ai-mapping","bases":["ai-mapping"],"basisDetail":"claude-haiku-5-5: Remote unauthenticated deserialization exploit against public-facing app","mappingType":"exploitation_technique","evidence":[{"from":"description","quote":"Deserialization of Untrusted Data due to the possibility of deserialization of arbitrary .NET classes","start":52,"end":153}],"model":"claude-haiku-5-5","confidence":"medium","confidenceNote":"AI-mapped from the description (quote-validated, not expert-reviewed)"},{"id":"T1059","name":"Command and Scripting Interpreter","tactics":["execution"],"provenance":"ai","basis":"ai-mapping","bases":["ai-mapping"],"basisDetail":"claude-haiku-5-5: Deserialization yields arbitrary code execution","mappingType":"primary_impact","evidence":[{"from":"description","quote":"can be abused to gain remote code execution","start":161,"end":204}],"model":"claude-haiku-5-5","confidence":"medium","confidenceNote":"AI-mapped from the description (quote-validated, not expert-reviewed)"}],"reports":[],"affected":[{"ecosystem":"NuGet","package":"AjaxNetProfessional","vulnerableRanges":["<21.11.29.1"],"patched":["21.11.29.1"],"from":["GHSA-6r7c-6w96-8pvw"],"provenance":"source"}],"advisories":[{"id":"GHSA-6r7c-6w96-8pvw","url":"https://github.com/advisories/GHSA-6r7c-6w96-8pvw","severity":"CRITICAL","ecosystem":"NuGet","package":"AjaxNetProfessional","vulnerableRanges":["<21.11.29.1"],"patched":["21.11.29.1"],"provenance":"source","from":"GHSA"}],"euvd":{"id":"EUVD-2021-2466","url":"https://euvd.enisa.europa.eu/vulnerability/EUVD-2021-2466","exploited":true,"exploitedSince":"2026-08-26","provenance":"source"},"exploits":[],"exploitSources":{"pocGithub":{"count":1,"skipped":0,"earliest":"2021-12-15","earliestUrl":"https://github.com/numanturle/CVE-2021-23758-POC","repos":[{"name":"numanturle/CVE-2021-23758-POC","url":"https://github.com/numanturle/CVE-2021-23758-POC","stars":18,"created":"2021-12-15"}]},"metasploit":[{"name":"AjaxPro Deserialization Remote Code Execution","module":"exploit/windows/http/ajaxpro_deserialization_rce","type":"exploit","disclosureDate":"2021-12-03","url":"https://github.com/rapid7/metasploit-framework/blob/master/modules/exploits/windows/http/ajaxpro_deserialization_rce.rb"}],"first":{"date":"2021-12-03","source":"Metasploit","url":"https://github.com/rapid7/metasploit-framework/blob/master/modules/exploits/windows/http/ajaxpro_deserialization_rce.rb"},"provenance":"source"},"exploitRefs":["http://packetstormsecurity.com/files/175677/AjaxPro-Deserialization-Remote-Code-Execution.html","https://blog.talosintelligence.com/uat-10147-chinese-speaking-adversary-integrates-agentic-ai-into-post-compromise-operations/"],"flow":[{"stage":"exploitation","techniques":["T1190"],"provenance":"ai"},{"stage":"primary","techniques":["T1059"],"provenance":"ai"}],"timeline":[{"date":"2021-12-03","kind":"published","label":"Published (NVD)","url":"https://nvd.nist.gov/vuln/detail/CVE-2021-23758","provenance":"source"},{"date":"2021-12-03","kind":"exploit-public","label":"First public exploit: Metasploit; later: PoC-in-GitHub 2021-12-15","url":"https://github.com/rapid7/metasploit-framework/blob/master/modules/exploits/windows/http/ajaxpro_deserialization_rce.rb","provenance":"source"},{"date":"2026-08-20","kind":"exploited-reported","label":"Exploitation first reported (VulnCheck KEV evidence)","url":"https://blog.talosintelligence.com/uat-10147-chinese-speaking-adversary-integrates-agentic-ai-into-post-compromise-operations/","provenance":"source"},{"date":"2026-08-26","kind":"kev","label":"Added to CISA KEV","url":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","provenance":"source"},{"date":"2026-08-26","kind":"euvd-exploited","label":"ENISA EUVD: exploited","url":"https://euvd.enisa.europa.eu/vulnerability/EUVD-2021-2466","provenance":"source"}],"speed":{"daysToPublicExploit":0,"firstExploitFrom":"Metasploit","daysToKev":1727},"priority":{"score":79.8,"factors":[{"name":"In a KEV catalog","points":35.0,"detail":"listed in CISA KEV and VulnCheck KEV"},{"name":"Recent KEV listing","points":10.0,"detail":"added 71 days ago"},{"name":"Known ransomware use","points":0.0,"detail":"not known"},{"name":"EPSS percentile","points":19.93,"detail":"percentile 0.9966"},{"name":"Named in threat reports","points":0.0,"detail":"0 reports"},{"name":"Public exploit code","points":5.0,"detail":"2 NVD references tagged Exploit; 1 PoC-in-GitHub repo; 1 Metasploit module"},{"name":"Mentioned in OTX pulses","points":3.0,"detail":"34 pulses"},{"name":"CVSS severity","points":6.86,"detail":"base score 9.8"},{"name":"End-of-life product","points":0.0,"detail":"supported or unknown"}]},"lineage":{"familyId":"fam-michaelschwarz-ajax-net-professional-cve-2021-23758","children":[{"from":"CVE-2021-23758","to":"CVE-2021-43853","relation":"successor","confidence":"high","kind":"lineage","evidence":[{"kind":"version-step","provenance":"source","package":"NuGet:AjaxNetProfessional","fromFixed":"21.11.29.1","toFixed":"21.12.22.1","daysApart":19},{"kind":"same-code","provenance":"machine","files":["AjaxPro/Utilities/Constant.cs","AjaxPro/core.js"],"commits":["https://github.com/michaelschwarz/Ajax.NET-Professional/commit/b0e63be5f0bb20dfce507cb8a1a9568f6e73de57","https://github.com/michaelschwarz/Ajax.NET-Professional/commit/c89e39b9679fcb8ab6644fe21cc7e652cb615e2b"],"basis":"shared function","functions":["Constant","extend"]},{"kind":"similar","provenance":"machine","score":0.24,"basis":"same package + description similarity"}]},{"from":"CVE-2021-23758","to":"CVE-2023-49289","relation":"related","confidence":"medium","kind":"lineage","evidence":[{"kind":"same-code","provenance":"machine","files":["AjaxPro/Utilities/Constant.cs","AjaxPro/core.js"],"commits":["https://github.com/michaelschwarz/Ajax.NET-Professional/commit/b0e63be5f0bb20dfce507cb8a1a9568f6e73de57","https://github.com/michaelschwarz/Ajax.NET-Professional/commit/c89e39b9679fcb8ab6644fe21cc7e652cb615e2b"],"basis":"shared function","functions":["Constant","extend"]}]}],"packageHistory":[{"cve":"CVE-2021-23758","published":"2021-12-03","fixed":"21.11.29.1","kev":true},{"cve":"CVE-2021-43853","published":"2021-12-22","fixed":"21.12.22.1","kev":false},{"cve":"CVE-2023-49289","published":"2023-12-04","fixed":"21.12.22.1","kev":false}],"package":"NuGet:AjaxNetProfessional"}}