CVE-2021-23758UnknownPublished 19 Jan 2026

tlp clear · KRVTZ IDS alerts for 2026-01-19

Affects tlp clearSource CIRCL OSINT Feed

TLP:CLEAR, disclosure is not limited

Authoritative record:CVE-2021-23758· High 8.1

Exploited in the wild · KEV due 9 Sep 2026 · public exploit available (Metasploit) · 82% EPSS : block it and hunt for it in your logs now.

Data as of 26 Oct 2026, 07:57 UTC

CVSS base score

8.1High

How severe the flaw is on the 0–10 CVSS scale.

KEV deadline: 9 Sep 2026 US federal agencies must patch by this date; a sensible deadline for everyone else.
EPSS: 82.5% chance of exploitation in 30 days – higher than 99% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

Exploitation evidence

t = 0 is the CVE’s publication on cve.org

Disclosed: evidence found.
CVE published 3 Dec 2021
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: evidence found.
1 Metasploit module
Exploited in the wildExploited: evidence found.
Listed in CISA KEV 4.7 years after disclosure
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

CVE published
on cve.org
2021-12-0320:05Z, t = 0
Added to CISA KEV (opens in a new tab)
exploitation confirmed
2026-08-26, 4.7 years after disclosure
KEV remediation due
US federal deadline
2026-09-09, 4.8 years after disclosure

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), CISA KEV (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 2026-10-26.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

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.

Affected software

Product	Affected	Fixed in
AjaxPro.2	Affected =0	Fixed in–

Description

The KRVTZ IDS alerts from January 19, 2026, report low-severity reconnaissance and scanning activities targeting AjaxPro Remote Code Execution vulnerability (CVE-2021-23758) and IIS 8.3 web servers. These include brute force attempts, suspicious user-agent strings linked to InfoBot malware, and directory brute forcing. No active exploits or patches are currently associated with these alerts, but early-stage probing could lead to more serious attacks. European countries such as Germany, France, the UK, Netherlands, Italy, Spain, and Poland are highlighted as likely affected due to market presence. The overall threat severity is medium given the potential impact if exploitation occurs.

Impact

The impact is currently low-severity reconnaissance and scanning activities, but the presence of public exploit code and known reconnaissance attempts increases the risk of successful exploitation. If exploited, the AjaxPro Remote Code Execution vulnerability could allow remote code execution, potentially leading to system compromise. The alerts also indicate brute force attempts and InfoBot malware-related activity, which could facilitate unauthorized access or malware infection. The threat is particularly relevant to European organizations running IIS 8.3 or AjaxPro components.

Defensive guidance

Organizations should maintain vigilant monitoring and implement targeted defenses against brute force and scanning activities. Sharing threat intelligence and applying network-level protections to detect and block suspicious traffic related to InfoBot malware and brute force attempts are recommended.

CWE-502Deserialization of Untrusted Data (opens in a new tab)
Base weaknessLikelihood of exploit: MediumCWE Top 25 (2025): #15OWASP Top 10 A08:2025: Software or Data Integrity Failures (opens in a new tab)
The product deserializes untrusted data without sufficiently ensuring that the resulting data will be valid.
Architecture and Design · Implementation
If available, use the signing/sealing features of the programming language to assure that deserialized data has not been tainted. For example, a hash-based message authentication code (HMAC) could be used to ensure that data has not been modified.
Implementation
When deserializing data, populate a new object rather than just deserializing. The result is that the data flows through safe input validation and that the functions are safe.
Implementation
Explicitly define a final object() to prevent deserialization.
OWASP Cheat Sheets
Abuse Case (opens in a new tab)
Deserialization (opens in a new tab)
XML Security (opens in a new tab)
XML External Entity Prevention (opens in a new tab)
Software Supply Chain Security (opens in a new tab)
OWASP ASVS 4.0.3
V1.5.2 (opens in a new tab)
V5.5.3 (opens in a new tab)
V5.5.1 (opens in a new tab)
Attack patterns
Object Injection (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

Indicators of compromise

IP addresses 4

34.207.235.82haproxy: 34.207.235.82 connecting to (submission/TCP) 15x in hour, possible bruteforcing.
45.13.189.123ET EXPLOIT AjaxPro RCE Attempt (CVE-2021-23758)
34.26.155.186ET USER_AGENTS Suspicious User-Agent (InfoBot)
192.168.144.78ET WEB_SERVER IIS 8.3 Filename With Wildcard (Possible File/Dir Bruteforce)

Community reviews

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Exploitation evidence

Timeline

What to do

Affected software

Description

AI analysisMachine-generated, updated 25 Oct 2026, 21:15 UTC

Public exploits and detection1 Metasploit module

WeaknessesCWE-502

Indicators of compromise

IP addresses 4

Community reviews

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