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Merge pull request #21807 from owen-mc/java/improve-qhelp-unsafe-deserialization

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Shared: improve qhelp for unsafe deserialization queries
This commit is contained in:
Owen Mansel-Chan
2026-05-12 22:22:49 +01:00
committed by GitHub
parent 5508b1576f a5ef036465
commit 0b808e1170
5 changed files with 67 additions and 14 deletions
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29
java/ql/src/Security/CWE/CWE-502/UnsafeDeserialization.qhelp
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@@ -5,26 +5,37 @@
<p>
Deserializing untrusted data using any deserialization framework that
allows the construction of arbitrary serializable objects is easily exploitable
and in many cases allows an attacker to execute arbitrary code. Even before a
and in many cases allows an attacker to execute arbitrary code. Even before a
deserialized object is returned to the caller of a deserialization method a lot
of code may have been executed, including static initializers, constructors,
and finalizers. Automatic deserialization of fields means that an attacker may
and finalizers. Automatic deserialization of fields means that an attacker may
craft a nested combination of objects on which the executed initialization code
may have unforeseen effects, such as the execution of arbitrary code.
</p>
<p>
There are many different serialization frameworks. This query currently
There are many different serialization frameworks. This query currently
supports Kryo, XmlDecoder, XStream, SnakeYaml, JYaml, JsonIO, YAMLBeans, HessianBurlap, Castor, Burlap,
Jackson, Jabsorb, Jodd JSON, Flexjson, Gson, JMS, and Java IO serialization through
<code>ObjectInputStream</code>/<code>ObjectOutputStream</code>.
</p>
<p>
Note that a deserialization method is only dangerous if it can instantiate
arbitrary classes. Serialization frameworks that use a schema to instantiate
only expected, predefined types are generally not tracked by this query. For
example, Apache Avro's deserialization methods follow a schema and are
therefore generally safe with respect to arbitrary-class-instantiation and
gadget-chain attacks when the schema is trusted and does not permit
user-controlled type resolution. However, care must be taken to ensure the schema
strictly limits the allowed types. Permitting common standard library classes
can still leave the application vulnerable to gadget-chain attacks.
</p>
</overview>
<recommendation>
<p>
Avoid deserialization of untrusted data if at all possible. If the
Avoid deserialization of untrusted data if at all possible. If the
architecture permits it then use other formats instead of serialized objects,
for example JSON or XML. However, these formats should not be deserialized
for example JSON or XML. However, these formats should not be deserialized
into complex objects because this provides further opportunities for attack.
For example, XML-based deserialization attacks
are possible through libraries such as XStream and XmlDecoder.
@@ -43,7 +54,7 @@ Recommendations specific to particular frameworks supported by this query:
<li><b>Recommendation</b>: Call <code>com.alibaba.fastjson.parser.ParserConfig#setSafeMode</code> with the argument <code>true</code> before deserializing untrusted data.</li>
</ul>
<p></p>
<p><b>FasterXML</b> - <code>com.fasterxml.jackson.core:jackson-databind</code></p>
<p><b>FasterXML</b> - <code>com.fasterxml.jackson.core:jackson-databind</code></p>
<ul>
<li><b>Secure by Default</b>: Yes</li>
<li><b>Recommendation</b>: Don't call <code>com.fasterxml.jackson.databind.ObjectMapper#enableDefaultTyping</code> and don't annotate any object fields with <code>com.fasterxml.jackson.annotation.JsonTypeInfo</code> passing either the <code>CLASS</code> or <code>MINIMAL_CLASS</code> values to the annotation.
@@ -56,16 +67,16 @@ Recommendations specific to particular frameworks supported by this query:
<li><b>Recommendation</b>: Don't call <code>com.esotericsoftware.kryo(5).Kryo#setRegistrationRequired</code> with the argument <code>false</code> on any <code>Kryo</code> instance that may deserialize untrusted data.</li>
</ul>
<p></p>
<p><b>ObjectInputStream</b> - <code>Java Standard Library</code></p>
<p><b>ObjectInputStream</b> - <code>Java Standard Library</code></p>
<ul>
<li><b>Secure by Default</b>: No</li>
<li><b>Recommendation</b>: Use a validating input stream, such as <code>org.apache.commons.io.serialization.ValidatingObjectInputStream</code>.</li>
<li><b>Recommendation</b>: Use a validating input stream, such as <code>org.apache.commons.io.serialization.ValidatingObjectInputStream</code>.</li>
</ul>
<p></p>
<p><b>SnakeYAML</b> - <code>org.yaml:snakeyaml</code></p>
<ul>
<li><b>Secure by Default</b>: As of version 2.0.</li>
<li><b>Recommendation</b>: For versions before 2.0, pass an instance of <code>org.yaml.snakeyaml.constructor.SafeConstructor</code> to <code>org.yaml.snakeyaml.Yaml</code>'s constructor before using it to deserialize untrusted data.</li>
<li><b>Recommendation</b>: For versions before 2.0, pass an instance of <code>org.yaml.snakeyaml.constructor.SafeConstructor</code> to <code>org.yaml.snakeyaml.Yaml</code>'s constructor before using it to deserialize untrusted data.</li>
</ul>
<p></p>
<p><b>XML Decoder</b> - <code>Standard Java Library</code></p>