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CVE-2021-23758 (GCVE-0-2021-23758)

Vulnerability from cvelistv5 – Published: 2021-12-03 20:05 – Updated: 2026-08-27 03:56
VLAI CISA Previdian
Title
Deserialization of Untrusted Data
Summary
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.
Severity
8.1 (High)
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
SSVC
Exploitation: active Automatable: no Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-08-26 00:00 UTC
CWE
  • Deserialization of Untrusted Data
  • CWE-502 - Deserialization of Untrusted Data
Assigner
References
Impacted products
Vendor Product Version CPE status
n/a AjaxPro.2 Affected: 0 , < unspecified (custom)
Date Public
2021-12-03 00:00
Credits
Hans-Martin Münch (MOGWAI LABS)
CISA
Known Exploited Vulnerability - GCVE BCP-07 Compliant
KEV entry ID: a6478612-57d7-4215-ae14-6e1cb7e92f74

Vulnerability ID: CVE-2021-23758

Status: Confirmed

Status Updated: 2026-08-26 00:00 UTC

Exploited: Yes

Timestamps
First Seen: 2026-08-26
Asserted: 2026-08-26
Scope
Notes: Ajax.NET Professional Deserialization of Untrusted Data Vulnerability | Affected: Ajax.NET Professional / Ajax.NET Professional | Description: Ajax.NET Professional (AjaxPro) contains a deserialization of untrusted data vulnerability that could allow for remote code execution via arbitrary .NET classes. The impacted product(s) could be end-of-life (EoL) and/or end-of-service (EoS). Users are advised to discontinue use and/or transition to a supported version. | Required action: 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. | Due date: 2026-09-09 | Known ransomware campaign use (KEV): Unknown | Notes (KEV): 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
Evidence

Type: Vendor Report

Signal: Successful Exploitation

Confidence: 80%

Source: cisa-kev

Details
Cwes CWE-502
Feed CISA Known Exploited Vulnerabilities Catalog
Product Ajax.NET Professional
Due Date 2026-09-09
Date Added 2026-08-26
Vendorproject Ajax.NET Professional
Vulnerabilityname Ajax.NET Professional Deserialization of Untrusted Data Vulnerability
Knownransomwarecampaignuse Unknown
References
Created: 2026-08-26 18:00 UTC | Updated: 2026-08-26 18:00 UTC
Previdian
Known Exploited Vulnerability - GCVE BCP-07 Compliant
KEV entry ID: 3b82890a-b32d-4df3-a18a-7bef29f093cb

Vulnerability ID: CVE-2021-23758

Status: Confirmed

Status Updated: 2026-08-26 17:00 UTC

Exploited: Yes

Timestamps
First Seen: 2026-08-26
Asserted: 2026-08-26
Scope
Notes: Deserialization of Untrusted Data | Affected: michaelschwarz / AjaxPro.2 | CVSS: 8.1 (HIGH) | EPSS: 0.89096 | Used in malware: unknown | Not yet in CISA KEV: False
Evidence

Type: Public Report

Signal: Successful Exploitation

Confidence: 70%

Source: previdian

Details
Feed Previdian (previdian.com)
Title Deserialization of Untrusted Data
Vendor michaelschwarz
Product AjaxPro.2
Added Date 2026-08-26T17:00:09.897Z
Cvss Score 8.1
Epss Score 0.89096
Cvss Severity HIGH
Epss Percentile 0.99768
Used In Malware unknown
Ahead Of Cisa Kev None
Not Yet In Cisa Kev False
References
Created: 2026-08-27 18:00 UTC | Updated: 2026-08-27 18:00 UTC
Show details on NVD website
To clipboard 

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      "containers": "{\"adp\": [{\"title\": \"CVE Program Container\", \"references\": [{\"url\": \"https://snyk.io/vuln/SNYK-DOTNET-AJAXPRO2-1925971\", \"tags\": [\"x_transferred\"]}, {\"url\": \"https://github.com/michaelschwarz/Ajax.NET-Professional/commit/b0e63be5f0bb20dfce507cb8a1a9568f6e73de57\", \"tags\": [\"x_transferred\"]}, {\"url\": \"http://packetstormsecurity.com/files/175677/AjaxPro-Deserialization-Remote-Code-Execution.html\", \"tags\": [\"x_transferred\"]}], \"providerMetadata\": {\"orgId\": \"af854a3a-2127-422b-91ae-364da2661108\", \"shortName\": \"CVE\", \"dateUpdated\": \"2024-08-03T19:14:09.129Z\"}}, {\"title\": \"CISA ADP Vulnrichment\", \"metrics\": [{\"other\": {\"type\": \"ssvc\", \"content\": {\"id\": \"CVE-2021-23758\", \"role\": \"CISA Coordinator\", \"options\": [{\"Exploitation\": \"active\"}, {\"Automatable\": \"no\"}, {\"Technical Impact\": \"total\"}], \"version\": \"2.0.3\", \"timestamp\": \"2026-08-26T17:44:04.350622Z\"}}}, {\"other\": {\"type\": \"kev\", \"content\": {\"dateAdded\": \"2026-08-26\", \"reference\": \"https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-23758\"}}}], \"references\": [{\"url\": \"https://blog.talosintelligence.com/uat-10147-chinese-speaking-adversary-integrates-agentic-ai-into-post-compromise-operations/\", \"tags\": [\"third-party-advisory\"]}, {\"url\": \"https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-23758\", \"tags\": [\"government-resource\"]}], \"problemTypes\": [{\"descriptions\": [{\"lang\": \"en\", \"type\": \"CWE\", \"cweId\": \"CWE-502\", \"description\": \"CWE-502 Deserialization of Untrusted Data\"}]}], \"providerMetadata\": {\"orgId\": \"134c704f-9b21-4f2e-91b3-4a467353bcc0\", \"shortName\": \"CISA-ADP\", \"dateUpdated\": \"2026-08-26T13:15:45.695Z\"}, \"timeline\": [{\"lang\": \"en\", \"time\": \"2026-08-26T00:00:00.000Z\", \"value\": \"CVE-2021-23758 added to CISA KEV\"}]}], \"cna\": {\"title\": \"Deserialization of Untrusted Data\", \"credits\": [{\"lang\": \"en\", \"value\": \"Hans-Martin M\\u00fcnch (MOGWAI LABS)\"}], \"metrics\": [{\"cvssV3_1\": {\"scope\": \"UNCHANGED\", \"version\": \"3.1\", \"baseScore\": 8.1, \"attackVector\": \"NETWORK\", \"baseSeverity\": \"HIGH\", \"vectorString\": \"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H\", \"integrityImpact\": \"HIGH\", \"userInteraction\": \"NONE\", \"attackComplexity\": \"HIGH\", \"availabilityImpact\": \"HIGH\", \"privilegesRequired\": \"NONE\", \"confidentialityImpact\": \"HIGH\"}}], \"affected\": [{\"vendor\": \"n/a\", \"product\": \"AjaxPro.2\", \"versions\": [{\"status\": \"affected\", \"version\": \"0\", \"lessThan\": \"unspecified\", \"versionType\": \"custom\"}]}], \"datePublic\": \"2021-12-03T00:00:00.000Z\", \"references\": [{\"url\": \"https://snyk.io/vuln/SNYK-DOTNET-AJAXPRO2-1925971\"}, {\"url\": \"https://github.com/michaelschwarz/Ajax.NET-Professional/commit/b0e63be5f0bb20dfce507cb8a1a9568f6e73de57\"}, {\"url\": \"http://packetstormsecurity.com/files/175677/AjaxPro-Deserialization-Remote-Code-Execution.html\"}], \"descriptions\": [{\"lang\": \"en\", \"value\": \"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.\"}], \"problemTypes\": [{\"descriptions\": [{\"lang\": \"en\", \"type\": \"text\", \"description\": \"Deserialization of Untrusted Data\"}]}], \"providerMetadata\": {\"orgId\": \"bae035ff-b466-4ff4-94d0-fc9efd9e1730\", \"shortName\": \"snyk\", \"dateUpdated\": \"2023-11-14T03:06:35.776Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2021-23758\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-08-26T19:58:23.426Z\", \"dateReserved\": \"2021-01-08T00:00:00.000Z\", \"assignerOrgId\": \"bae035ff-b466-4ff4-94d0-fc9efd9e1730\", \"datePublished\": \"2021-12-03T20:05:12.932Z\", \"assignerShortName\": \"snyk\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}



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Taxonomy of the tags.





Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

Author Source Type Date Other

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.


Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.