Missing authentication
A sensitive function is reachable without proving who is using it.
CWE-306 · NVD record: nvd@nist.gov
Reading and practice labs · Free account for labs. Basic HTTP knowledge; some labs use Burp Suite.
Exploited. On CISA's list since 2023-03-10.
XStream Remote Code Execution Vulnerability
CVE-2021-39144 · XStream XStream · Published 2021-08-23
How bad would it be?
8.5 out of 10
CVSS rates it high.
How likely is it to be used?
98%
Estimated chance of exploitation in the next 30 days, among the top 1% of all scored flaws (EPSS, 2026-10-29).
Is it already being used?
Yes
CISA has seen it exploited in real attacks. For US government agencies the fix is deadline passed 1309 days ago (2023-03-31).
What CISA says to do
Apply updates per vendor instructions.
XStream contains a remote code execution vulnerability that allows an attacker to manipulate the processed input stream and replace or inject objects that result in the execution of a local command on the server. This vulnerability can affect multiple products, including but not limited to VMware Cloud Foundation.
What the flaw is
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.
From the NVD.
Fixes and advisories
Learn this
Explore this week’s weaknesses and all learning topics
Understand the kind of weakness behind this flaw. These resources teach the weakness, rather than reproduce this specific CVE. Follow the vendor's advice above to fix the affected product.
Insecure deserialization
Rebuilding objects from untrusted saved data can trigger unintended behaviour.
CWE-502 · CISA KEV; NVD record: nvd@nist.gov; NVD record: security-advisories@github.com
Reading and practice labs · Free account for labs. Basic HTTP knowledge; some labs use Burp Suite.
CWE-94 · CISA KEV; NVD record: security-advisories@github.com. We have not selected a close learning match for this label.
CWE is a catalogue of weakness types. Labels come from the sources shown and can differ or change. Resource matches reviewed 16 October 2026.
On SentryFeed
No story in the last 14 days has mentioned it.
Exploited flaws from CISA's KEV catalogue. Chance of exploitation from EPSS by FIRST. Descriptions and scores from the NVD. This product uses the NVD API but is not endorsed or certified by the NVD.