For years, Python has been the go-to language for developers who value speed and simplicity. Its clean syntax and massive ecosystem make it easy to get things done fast.
The newly disclosed CVE-2025-61765 flaw in the python-socketio library drives that point home. The bug is a remote code execution risk tied to how certain servers handle serialized data. But the real story runs deeper. It exposes how easily developers can put blind trust in what feels like “internal” code paths—systems assumed to be safe because they sit behind the firewall. That assumption, as this case shows, is anything but safe.
How a Trusted Library Turned Risky
BlueRock researchers discovered that versions of python-socketio prior to 5.14.0 could allow remote code execution under specific conditions. The problem centered on how the library used Python’s pickle module to serialize messages passed through shared message queues. When a message arrived, the system would automatically “unpickle” it, essentially re-creating Python objects from the transmitted data.
That behavior is fine in a fully trusted environment. But if an attacker gains access to the message queue, they can inject a malicious payload that executes the moment it’s read. In practical terms, that means arbitrary code could run on a targeted server without ever touching its web interface.
The flaw has been given a CVSS score of 6.4, reflecting that it requires prior access to the broker. BlueRock coordinated disclosure with the developers, who moved quickly once notified.
“This is about making an existing compromise worse, since the attack requires adding messages to back-end queues, rather than simply making a request to a website,” said Michael King, Senior Solutions Engineer at Black Duck. He added, “The fix is simple and it's already been released: change the word ‘pickle’ to the word ‘json’ in a few places, to ensure information is transmitted in a non-executable format.”
The Danger Built Into Pickle
Python’s pickle module was designed to make life easier for developers. It converts complex Python objects into byte streams that can be stored or sent elsewhere and then reconstituted later. The problem is that the process isn’t just about data; it can execute code as part of the rebuild. That’s fine if you’re loading objects you created yourself. It’s dangerous if you’re not.
BlueRock notes that the pickle module was designed for storing trusted Python objects, not for exchanging data between systems. Yet python-socketio client managers were using it that way—indiscriminately unpickling every message from shared brokers, even if those messages came from untrusted sources. If one of those brokers is compromised, or if a tenant in a shared environment turns hostile, the results can be catastrophic.
Who’s Exposed—and How
The python-socketio library powers a wide range of real-time applications, ranging from chat platforms and live dashboards to microservices that exchange data across containers. In large deployments, these systems often rely on shared message queues such as Redis, RabbitMQ, or Kafka to pass updates between servers. That’s where the risk comes in.
To exploit CVE-2025-61765, an attacker needs access to the underlying broker. But in multi-tenant environments, container clusters, or networks already breached through another vector, that barrier can be surprisingly low. Once an attacker reaches the queue, they can plant a payload that executes automatically when the next process reads it.
From there, the possibilities expand quickly: stealing credentials from environment variables, dropping persistence hooks, or pivoting deeper into the network. What began as a flaw in message serialization can easily become a platform for lateral movement or privilege escalation, especially in systems where multiple services share the same broker.
Fixing the Flaw
BlueRock reported the flaw to the python-socketio maintainers through a coordinated disclosure process. The team confirmed the issue quickly and released version 5.14.0, which changes how interprocess messages are handled to eliminate unsafe deserialization.
BlueRock’s advisory recommends that organizations upgrade immediately, then audit their environments for any use of older library versions. Beyond patching, the fix depends on tightening the boundaries around the message broker itself. Limit access to private networks, enforce strong authentication, and remove any shared or anonymous publishers. Logging and monitoring should be expanded to catch signs of tampering, such as unexpected pickle errors, worker restarts, or unexplained outbound connections.
The Bigger Lesson Behind the Bug
The CVE-2025-61765 flaw exposes how deeply trust is built into developer culture. Many development teams still operate under the assumption that what happens inside their network is inherently safe. That idea might have held up when applications lived on a single server, but in today’s distributed, containerized world, “internal” often includes dozens of services, brokers, and CI pipelines, some running in environments the organization doesn’t fully control.
This kind of implicit trust is what zero-trust advocates have been warning about for years. The notion that security can stop at the perimeter is outdated. Attackers routinely exploit weak internal links—shared credentials, open message queues, misconfigured service accounts—to move laterally and escalate privileges once they’re inside. A deserialization flaw in one microservice can become a launchpad for a broader compromise, just as a poisoned software dependency can cascade through a supply chain.
The lesson for developers is to treat every communication channel, even internal ones, as potentially hostile. Use safe, deterministic serialization formats like JSON or Protobuf. Validate data before processing. And design systems with security-by-default. The productivity culture that made Python so popular doesn’t have to come at the expense of safety, but it does require developers to rethink what “trusted” really means.
