`CVE-2020-26258` XStream

Affected software	XStream
Severity	7.7 High CVSS 3.1 3 scores
Fixed in	`1.4.15`
Weakness	Server-side request forgery (CWE-918)
Published	16 Dec 2020
Updated	13 Nov 2026

Description

XStream is a Java library to serialize objects to XML and back again. In XStream before version 1.4.15, a Server-Side Forgery Request vulnerability can be activated when unmarshalling. The vulnerability may allow a remote attacker to request data from internal resources that are not publicly available only by manipulating the processed input stream. If you rely on XStream's default blacklist of the Security Framework, you will have to use at least version 1.4.15. The reported vulnerability does not exist if running Java 15 or higher. No user is affected who followed the recommendation to setup XStream's Security Framework with a whitelist! Anyone relying on XStream's default blacklist can immediately switch to a whilelist for the allowed types to avoid the vulnerability. Users of XStream 1.4.14 or below who still want to use XStream default blacklist can use a workaround described in more detailed in the referenced advisories.

Exploitation status

Working exploit published

A reviewed exploit catalogue lists ready-to-run exploit code for this CVE.

CISA KEV not listed
VulnCheck KEV not listed
CISA Vulnrichment exploitation: none
Indexed PoC 2 indexed Published artifacts you can open, in GitHub PoC, Nuclei; first seen 2021-01-22.
EPSS 82% chance in 30 days A model's forecast, not a report of exploitation. Higher than 99.7% of all scored CVEs.

1 of these are GitHub repositories with fewer than 5 stars. They are listed for reference and don't count toward the exploitation status above.

Index	Artifact	Stars	First seen
GitHub PoC	CVE-2020-26258 && XStream SSRF		2021-01-22
Nuclei	XStream <1.4.15 - Server-Side Request Forgery

Index

Artifact

Stars

First seen

GitHub PoC

CVE-2020-26258 && XStream SSRF

2021-01-22

Nuclei

XStream <1.4.15 - Server-Side Request Forgery

Waratek protection

Protected by Waratek

Waratek has a rule that blocks attacks on this vulnerability.

Protection full Deserialization
Action available security rule
Review human Researcher
Record active

Decided by	A researcher's recorded decision for this specific CVE
Finding	A researcher found this CVE protected by the ARMR Deserialization RCE rule.

Decided by

A researcher's recorded decision for this specific CVE

Finding

A researcher found this CVE protected by the ARMR Deserialization RCE rule.

Waratek research note

written 2026-11-13

Written by a Waratek engineer who reviewed this CVE. Their decision sets the status above, ahead of every automated rule except a withdrawal.

Comments

Rule Name: Deserialization RCE rule

How to mitigate CVE-2020-26258

Upgrade XStream to 1.4.15 or later. Until you can, Waratek RASP blocks exploitation with its deserialization rule. It runs inside the Java application, with no code changes.

Waratek RASP Runtime protection for Java applications

CVSS

7.7 HIGH v3.1 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N 3 metrics

We show the highest score from the newest CVSS version. Scores from different versions can't be compared, and the first score listed is sometimes a 0.0 placeholder.

Version Score Band Vector Assigner Type

CVSS 3.1 7.7 HIGH CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N NVD Primary published

CVSS 3.1 6.3 MEDIUM CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:N/A:N security-advisories@github.com Secondary

CVSS 2.0 5.0 none AV:N/AC:L/Au:N/C:P/I:N/A:N NVD Primary

Version	Score	Band	Vector	Assigner	Type
CVSS 3.1	7.7	HIGH	`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N`	NVD	Primary	published
CVSS 3.1	6.3	MEDIUM	`CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:N/A:N`	security-advisories@github.com	Secondary
CVSS 2.0	5.0	none	`AV:N/AC:L/Au:N/C:P/I:N/A:N`	NVD	Primary

Affected software and releases

Maven packages

Affected and fixed versions, from OSV.dev

Package Introduced Fixed Last affected

com.thoughtworks.xstream:xstream 0 1.4.15 unbounded

Package	Introduced	Fixed	Last affected
`com.thoughtworks.xstream:xstream`	0	`1.4.15`	unbounded

Products and versions

5 products, 8 version entries

Source	Vendor	Product	Scheme	Affected versions
nvd	apache	struts	generic	＜ 6.0.0
osv	com.thoughtworks.xstream	xstream	generic	＜ 1.4.15
nvd	debian	debian linux	generic	9.0 · 10.0
nvd	fedoraproject	fedora	generic	33 · 34 · 35
nvd	xstream	xstream	generic	＜ 1.4.15

Source

Vendor

Product

Scheme

Affected versions

nvd

apache

struts

generic

＜ 6.0.0

osv

com.thoughtworks.xstream

xstream

generic

＜ 1.4.15

nvd

debian

debian linux

generic

9.0 · 10.0

nvd

fedoraproject

fedora

generic

33 · 34 · 35

nvd

xstream

generic

＜ 1.4.15

References

URL	Tags
https://github.com/x-stream/xstream/security/advisories/GHSA-4cch-wxpw-8p28	WEB
https://github.com/x-stream/xstream	PACKAGE
https://lists.apache.org/thread.html/r97993e3d78e1f5389b7b172ba9f308440830ce5f051ee62714a0aa34%40%3Ccommits.struts.apache.org%3E	WEB
https://lists.apache.org/thread.html/r97993e3d78e1f5389b7b172ba9f308440830ce5f051ee62714a0aa34@%3Ccommits.struts.apache.org%3E	WEB
https://lists.debian.org/debian-lts-announce/2020/12/msg00042.html	WEB
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/22KVR6B5IZP3BGQ3HPWIO2FWWCKT3DHP	WEB
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/PVPHZA7VW2RRSDCOIPP2W6O5ND254TU7	WEB
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/QGXIU3YDPG6OGTDHMBLAFN7BPBERXREB	WEB
https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/22KVR6B5IZP3BGQ3HPWIO2FWWCKT3DHP	WEB
https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/PVPHZA7VW2RRSDCOIPP2W6O5ND254TU7	WEB

URL

Timeline

Published	2020-12-16	By the CVE Program.
NVD record modified	2026-10-07	NVD's own last-modified date for this record.
Classification created	2026-11-13	First commit adding this CVE's research note.
Last VRT activity	2026-11-13	Most recent commit touching this CVE's classification, patch or rule file.

Published

2020-12-16

By the CVE Program.

NVD record modified

2026-10-07

NVD's own last-modified date for this record.

Classification created

2026-11-13

First commit adding this CVE's research note.

Last VRT activity

2026-11-13

Most recent commit touching this CVE's classification, patch or rule file.

How VRT decided (4 of 24 rules ran)

4 of 24 rules ran. The rest didn't run because an earlier rule had already settled the CVE.

# Rule Outcome Status Detail

identity: Does this identifier describe a vulnerability at all? the first rule that matches decides

1 rejected no match CVE Program withdrawal of this identifier

scope: Is it a vulnerability Waratek protects? the first rule that matches decides

2 armr-patch-file no match An ARMR patch file on disk for this CVE

3 armr-secure-rule-file no match An ARMR security-rule template on disk for this CVE

4 manual-classification decided it matched Protected by Waratek A researcher found this CVE protected by the ARMR Deserialization RCE rule.

5 manual classification not reached Manual classification of this CVE in the legacy dataset

6 non-java-upstream not reached A root cause in non-Java code: an OS kernel, a C library, or a bundled runtime

7 oracle-component not reached The defect being in a component of a tracked product the agent does not reach: JavaFX, the Java SE installer, the JInitiator browser plug-in, the native WebLogic proxy plug-in, or a native part of Oracle Application Server or Collaboration Suite (HTTP Server, Web Cache, Internet Directory, mail and calendar servers). Oracle gives these no CPE of their own and names them only in the description.

8 java-client-side not reached Oracle's own risk-matrix note saying the CVE is reached only through untrusted code in the Java sandbox (applets, Web Start) or only through a client installation of Java, so a server running its own trusted code is not exposed

9 osv-maven not reached An OSV.dev record of this CVE affecting a package published to Maven Central. When every such package is one business applications do not use (Minecraft mods and launchers, Fastjson) and no tracked product is named by CPE, it settles the CVE as Outside Waratek scope instead

10 cna-maven-package not reached An affected Maven artifact named by the CNA itself

11 known-cpe-product not reached An NVD CPE naming a product ARMR tracks

12 cna-cpe-product not reached A CPE the CNA published naming a tracked product. Oracle publishes these on advisory day, months before NVD.

13 oracle-advisory-family not reached A tracked product family named in Oracle's own risk matrix. CPE cannot carry a suite name, only a module.

14 cna-named-product not reached A tracked product named in words by the CVE's own CNA, on a record with no CPE yet. Apache and Eclipse publish these on advisory day, before NVD adds CPE data.

15 non-deployable-product not reached The only affected product being a sealed appliance image, where Java runs but no -javaagent can be attached

16 unmatched-product not reached No tracked product matched above, and none present at all

disposition: What do we do about one that is? every rule runs

17 patch-hint not reached A reference pointing at the upstream fix: a commit, a PR, a Red Hat bug

18 open-source-maven not reached The affected package being open source on Maven, so the fix can be read

19 poc-derivable not reached An indexed exploit clearing the evidence bar to reverse-engineer, where there is no source to read

20 no-exploit not reached Nothing to build a rule from yet: no published exploit, no CISA record of exploitation and no source-level change to read

21 secure-rule-match not reached A vulnerability class already blocked by an ARMR security rule

22 exploited-no-fix-or-poc not reached Somebody exploiting this CVE (a CISA or VulnCheck KEV listing, or a CISA verdict of active exploitation), with no fix, source code or PoC to build a rule from

23 below-action-threshold not reached Medium or Low severity, no CISA or VulnCheck KEV listing, no PoC clearing the evidence bar, no CISA verdict, no Oracle advisory

24 no-exploit-published not reached Exploit code for this candidate, published in a reviewed catalogue or a GitHub repository with 5 or more stars, or in use per CISA or VulnCheck; not only a CISA verdict, a forecast, or nothing at all

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