XStream Remote Code Execution Vulnerability

Exploited · KEV 2023-03-10Metasploit moduleCVE-2021-39144CWE-94CWE-502

Exploited since 2023-03-10. No WAF vendor names it yet. Our CRS test: blocked.

Edge rules

0/8

Our test

Blocked

CVSS

8.5

EPSS

98.1% Top 0.1%

Posts, 14d

Published

2021-08-23

XStream is a simple library to serialize objects to XML and back again. In affected versions this vulnerability may allow a remote attacker has sufficient rights to execute commands of the host only by manipulating the processed input stream. No user is affected, who followed the recommendation to setup XStream's security framework with a whitelist limited to the minimal required types. XStream 1.4.18 uses no longer a blacklist by default, since it cannot be secured for general purpose.

Edge coverage

Claimed by vendors

CloudflareBefore feed historyOlder than its feedEnterprise: blocked · Free: passed AWSNo public claimNot namedWe measured: blocked Microsoft AzureNo public claimNot named Google CloudBefore feed historyOlder than its feedWe measured: blocked FastlyBefore feed historyOlder than its feed F5Before feed historyOlder than its feed AkamaiNo public sourceNo public changelog OWASP CRSBefore feed historyOlder than its feed

Ask Vigil

AI · answers from this page

Ask about CVE-2021-39144: who's covered, what to patch first, how vendors compare. I cite sources and won't help with attacks.

Workers AI (Llama 3.3). Can be wrong: check the cited source.

Severity, decoded

CVSS 3.1

8.5High

High · 8.5 / 10

Exploitable over the network under specific conditions, with low privileges and no user interaction, leading to full loss of confidentiality, integrity and availability, and the impact can reach components beyond the vulnerable one.

Over the internetAny user loginNo user actionHard to pull offSpreads beyond the appFull compromise

How the score is built8 metrics

Attack vectorAn attacker can reach it over the internet; no access to your network needed.
Network
Attack complexityThe attack only works when conditions outside the attacker's control line up.
High
Privileges requiredThe attacker needs an ordinary user account.
Low
User interactionNo one has to click or open anything; the attack works on its own.
None
ScopeThe attack can spread beyond the vulnerable component to other parts of the system.
Changed
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:H/PR:L/UI:N/S:C/C:H/I:H/A:H

CISA's assessmentSSVC, from the CVE record

ExploitationActive

Attackers are exploiting this in the wild.

AutomatableNo

At least one step needs hands-on work, which slows mass attacks.

Technical impactTotal

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

Public exploits

2 found

1 Metasploit0 Exploit-DB1 Scanner template0 GitHub PoCs

MetasploitVMware NSX Manager XStream unauthenticated RCE2022-10-25 · exploit · rank Excellent · has check
NucleiCVE-2021-39144.yamldetection template, replayed in our lab

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

Timeline

2021-08-23
CVE published
CVE List
2022-10-25
Metasploit module published
VMware NSX Manager XStream unauthenticated RCE
2023-03-10
Added to CISA KEV
Confirmed exploitation in the wild
2026-11-02
Our test: OWASP Core Rule Set blocked it
paranoia level 1, anomaly threshold 5, default CRS settings
2026-11-02
Our test: OWASP Core Rule Set blocked it
paranoia level 2, anomaly threshold 5, default CRS settings