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osvGoogleOSV:GHSA-MW36-7C6C-Q4Q2
HistoryNov 16, 2020 - 8:07 p.m.

XStream can be used for Remote Code Execution

2020-11-1620:07:59
Google
osv.dev
254

9.8 High

CVSS3

Attack Vector

NETWORK

Attack Complexity

LOW

Privileges Required

NONE

User Interaction

NONE

Scope

UNCHANGED

Confidentiality Impact

HIGH

Integrity Impact

HIGH

Availability Impact

HIGH

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

9.3 High

CVSS2

Access Vector

NETWORK

Access Complexity

MEDIUM

Authentication

NONE

Confidentiality Impact

COMPLETE

Integrity Impact

COMPLETE

Availability Impact

COMPLETE

AV:N/AC:M/Au:N/C:C/I:C/A:C

0.974 High

EPSS

Percentile

99.9%

Impact

The vulnerability may allow a remote attacker to run arbitrary shell commands only by manipulating the processed input stream.

Patches

If you rely on XStream’s default blacklist of the Security Framework, you will have to use at least version 1.4.14.

Workarounds

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 1.4.13 or below who still want to use XStream default blacklist can use a workaround depending on their version in use.

Users of XStream 1.4.13 can simply add two lines to XStream’s setup code:

xstream.denyTypes(new String[]{ "javax.imageio.ImageIO$ContainsFilter" });
xstream.denyTypes(new Class[]{ java.lang.ProcessBuilder.class });

Users of XStream 1.4.12 to 1.4.7 who want to use XStream with a black list will have to setup such a list from scratch and deny at least the following types: javax.imageio.ImageIO$ContainsFilter, java.beans.EventHandler, java.lang.ProcessBuilder, java.lang.Void and void.

xstream.denyTypes(new String[]{ "javax.imageio.ImageIO$ContainsFilter" });
xstream.denyTypes(new Class[]{ java.lang.ProcessBuilder.class, java.beans.EventHandler.class, java.lang.ProcessBuilder.class, java.lang.Void.class, void.class });

Users of XStream 1.4.6 or below can register an own converter to prevent the unmarshalling of the currently know critical types of the Java runtime. It is in fact an updated version of the workaround for CVE-2013-7285:

xstream.registerConverter(new Converter() {
  public boolean canConvert(Class type) {
    return type != null && (type == java.beans.EventHandler.class || type == java.lang.ProcessBuilder.class || type == java.lang.Void.class || void.class || type.getName().equals("javax.imageio.ImageIO$ContainsFilter") || Proxy.isProxy(type));
  }

  public Object unmarshal(HierarchicalStreamReader reader, UnmarshallingContext context) {
    throw new ConversionException("Unsupported type due to security reasons.");
  }

  public void marshal(Object source, HierarchicalStreamWriter writer, MarshallingContext context) {
    throw new ConversionException("Unsupported type due to security reasons.");
  }
}, XStream.PRIORITY_LOW);

Credits

Chen L found and reported the issue to XStream and provided the required information to reproduce it. He was supported by Zhihong Tian and Hui Lu, both from Guangzhou University.

References

See full information about the nature of the vulnerability and the steps to reproduce it in XStream’s documentation for CVE-2020-26217.

For more information

If you have any questions or comments about this advisory:

References

9.8 High

CVSS3

Attack Vector

NETWORK

Attack Complexity

LOW

Privileges Required

NONE

User Interaction

NONE

Scope

UNCHANGED

Confidentiality Impact

HIGH

Integrity Impact

HIGH

Availability Impact

HIGH

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

9.3 High

CVSS2

Access Vector

NETWORK

Access Complexity

MEDIUM

Authentication

NONE

Confidentiality Impact

COMPLETE

Integrity Impact

COMPLETE

Availability Impact

COMPLETE

AV:N/AC:M/Au:N/C:C/I:C/A:C

0.974 High

EPSS

Percentile

99.9%

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