Deserialization of Untrusted Data Affecting langgraph-checkpoint package, versions [,4.0.1rc1)
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
Do your applications use this vulnerable package?
In a few clicks we can analyze your entire application and see what components are vulnerable in your application, and suggest you quick fixes.
Test your applicationsSnyk Learn
Learn about Deserialization of Untrusted Data vulnerabilities in an interactive lesson.
Start learning- Snyk IDSNYK-PYTHON-LANGGRAPHCHECKPOINT-15433491
- published6 Mar 2026
- disclosed5 Mar 2026
- credityardenporat353
Introduced: 5 Mar 2026
CVE-2026-28277 (opens in a new tab)How to fix?
Upgrade langgraph-checkpoint to version 4.0.1rc1 or higher.
Overview
langgraph-checkpoint is a library with base interfaces for LangGraph checkpoint savers.
Affected versions of this package are vulnerable to Deserialization of Untrusted Data in the msgpack-encoded checkpoints. An attacker can execute arbitrary code by supplying a crafted msgpack-encoded payload to the persistence layer, which is then deserialized when loading checkpoints.
Note:
This is only exploitable if an attacker has the ability to modify checkpoint data in the backing store, such as after a database compromise or with privileged write access to the persistence layer.
Mitigations
LangGraph provides an allowlist-based hardening mechanism for msgpack checkpoint deserialization.
Strict mode (environment variable):
LANGGRAPH_STRICT_MSGPACKWhen set truthy (
1,true,yes), the default msgpack deserialization policy becomes strict.Concretely:
JsonPlusSerializer()will defaultallowed_msgpack_modulestoNone(strict) instead ofTrue(warn-and-allow), unless you explicitly passallowed_msgpack_modules=....allowed_msgpack_modules(serializer/checkpointer config):
This setting controls what msgpack “ext” types are allowed to be reconstructed.
True (default when strict mode is not enabled): allow all ext types, but log a warning when deserializing a type that is not explicitly registered.
None (strict): only a built-in safe set is reconstructed; other ext types are blocked.
[(module, class_name), ...] (strict allowlist): the built-in safe set plus exactly the listed symbols are reconstructed (exact-match).
Details
Serialization is a process of converting an object into a sequence of bytes which can be persisted to a disk or database or can be sent through streams. The reverse process of creating object from sequence of bytes is called deserialization. Serialization is commonly used for communication (sharing objects between multiple hosts) and persistence (store the object state in a file or a database). It is an integral part of popular protocols like Remote Method Invocation (RMI), Java Management Extension (JMX), Java Messaging System (JMS), Action Message Format (AMF), Java Server Faces (JSF) ViewState, etc.
Deserialization of untrusted data (CWE-502) is when the application deserializes untrusted data without sufficiently verifying that the resulting data will be valid, thus allowing the attacker to control the state or the flow of the execution.