CVE-2021-21342
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A Server-Side Forgery Request can be activated unmarshalling with XStream to access data streams from an arbitrary URL referencing a resource in an intranet or the local host
rank 45 = 12 + 23 + 0 + 10 + 0
rank@v1 · this cycle
Someone is already using it
CISA KEV catalog · public proof-of-concept · FIRST EPSS
EPSS 0.49990 · without this subject the record ranks 33
What it costs you if it fires
NVD CVSS base score, then the CNA's own
CVSS 9.1, from NVD · without this subject the record ranks 22
It is getting worse, not staying still
FIRST EPSS series, rescorings and bad loads removed
no persisting rise in 365 days · without this subject the record ranks 45
How much of the world it touches
NVD CPE configurations
20 products in the CPE ranges · without this subject the record ranks 35
Someone else already set the date
CISA KEV remediation due date
no CISA due date · without this subject the record ranks 45
$1.53M = $4.99M incident cost x 0.6121449559255632 exposure x 0.4999 likelihood
udv@v1 · unaudited · wrong for you until you say what you run
$4.99M is the cost of a breach that happened, from IBM Cost of a Data Breach Report 2026, global average. It is not the value of any asset of yours. That average already covers breaches of every severity, so scaling it by exposure understates a partial-impact record. That is an assumption, not a measurement. Your own asset value goes in the decision record.
Hindsight · the state
Foresight · where to check next
XStream is one instance of CWE-502, deserialization of untrusted data. The index holds 3288 prior instances of this class, 76 KEV-listed. 3 neighbors share the mechanism; each carries its own record state. taxonomy@v1
Sources disagree here.
Both shown, dated. We don't pick winners. disagreement-rules@v1
Running x-stream xstream? Check your version
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Harm, if it fires from the vector and the weakness
Written for the ticket you're about to file.
CISA KEV & Federal Remediation Deadline from the record and CISA
The fix, and how long it's been waiting.
Exploit Status & Known PoCs a ladder, not a score
Current rung: Nothing observed in held sources.
- RUNG 1Nothing observed in held sources
- RUNG 2Proof-of-concept published
- RUNG 3Exploited in the wild · CISA KEV listed
- RUNG 4Ransomware campaign use known
Affected & Fixed Versions as published
Show all 20 published ranges
A rung lights from a row in the index, never from an assessment. "Held sources" is the true scope of the claim: this index reads the CVE record, NVD, CISA KEV, FIRST's EPSS and public proof-of-concept repositories, and it does not observe attacks.
Attack path
What it is stated by the CNA
XStream is a Java library to serialize objects to XML and back again. In XStream before version 1.4.16, there is a vulnerability where the processed stream at unmarshalling time contains type information to recreate the formerly written objects. XStream creates therefore new instances based on these type information. An attacker can manipulate the processed input stream and replace or inject objects, that result in a server-side forgery request. No user is affected, who followed the recommendation to setup XStream's security framework with a whitelist limited to the minimal required types. receipt
Read the rest of the CNA's description
If you rely on XStream's default blacklist of the Security Framework, you will have to use at least version 1.4.16.
NVD's analysis a second authority
- severity
- 9.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
- weakness
- CWE-502; CWE-918
- affected versions
- xstream < 1.4.16; apache activemq < 5.15.14; apache activemq 5.16.0; and 17 more, listed in full below
- also scored by
- [email protected] 5.3 CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:N
The CNA scored it 5.3 and NVD 9.1. Both are shown because both were published; we do not pick one.
check it yourself x-stream.github.io x-stream.github.io github.com x-stream.github.io lists.debian.org lists.apache.org +9 morereceipt
Dated events
Movement the material steps
Show all 47 observations
47 observations held. A highlighted step crossed a promotion threshold. A step marked with a scoring model moved because the instrument was replaced, not because the vulnerability changed. receipt
The full biography
The record had been public for 5 years, 3 months when this index was last written.
The pattern, elsewhere
XStream is one instance of CWE-502, deserialization of untrusted data. The index holds 3288 prior instances of this class, 76 KEV-listed. 3 neighbors share the mechanism; each carries its own record state. [email protected]
3288 records in this class held. The six above are ranked by exploit maturity, then recency.
Siblings and hubs
Records related to this one
No record cites this identifier and it carries no alias. Its defect family is below.
Its defect family
x-stream xstream
Of the 5 records in this family that state one, this holds the highest NVD CVSS score: 9.1.
Grouped by shared product and weakness, not by shared vulnerability. Each record's own state is on its own page.
Family membership: held values
This record is one of a group, and the group's page describes all of them. This page is kept and dated, and the defect family's own page is the one we offer for indexing: the whole group.
Browse the index from here
These are index-wide views, not findings about CVE-2021-21342.
What usually comes next
Everything above needs no account. What is below is work: assembling it, scoping it to your estate, watching it, and handing it to someone else.