CVE-2026-25632: EPyT-Flow vulnerable to unsafe JSON deserialization (__type__)

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
• EPSS 1.4%, percentile 73: FIRST’s model estimates a 1.4% chance of exploitation activity in the next 30 days, higher than 73% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Only applies if your dependency tree includes epyt-flow (PyPI) < 0.16.1, fixed in 0.16.1. Check your lockfile, including transitive dependencies.

What it is

EPyT-Flow is a Python package designed for the easy generation of hydraulic and water quality scenario data of water distribution networks. Prior to 0.16.1, EPyT-Flow’s REST API parses attacker-controlled JSON request bodies using a custom deserializer (myloadfromjson) that supports a type field. When type is present, the deserializer dynamically imports an attacker-specified module/class and instantiates it with attacker-supplied arguments. This allows invoking dangerous classes such as subprocess.Popen, which can lead to OS command execution during JSON parsing. This also affects the loading of JSON files. This vulnerability is fixed in 0.16.1.

From the GitHub advisory

Impact EPyT-Flow’s REST API parses attacker-controlled JSON request bodies using a custom deserializer (myloadfromjson) that supports a type field. When type is present, the deserializer dynamically imports an attacker-specified module/class and instantiates it with attacker-supplied arguments. This allows invoking dangerous classes such as subprocess.Popen, which can lead to OS command execution during JSON parsing. This also affects the loading of JSON files.

Patches EPyT-Flow has been patched in 0.16.1 -- affects all versions

Workarounds Do not load any JSON from untrusted sources and do not expose the REST API.

Credits EPyT-Flow thanks Jarrett Chan (@syphonetic) for detecting and reporting the bug.

Weakness type: CWE-502.

Product: epyt-flow (PyPI) · Assigned by: GitHub_M · Published: 2026-02-06

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: none (no login)
• User interaction: none
• Scope: changed (can affect other components)

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation none, automatable yes, technical impact total.
• FIRST EPSS (model of 2026-10-21): 1.42% probability of exploitation activity in the next 30 days; percentile 73.

Timeline

• 2026-02-04 — GitHub-reviewed advisory GHSA-74vm-8frp-7w68 published (critical)
• 2026-02-06 — CVE record last updated
• 2026-02-06 — CVE record published by GitHub_M

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-74vm-8frp-7w68 github.com
2. CVE.org record CVE-2026-25632 cve.org
3. NVD entry CVE-2026-25632 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com
3. github.com github.com

Critical PyPI advisories · Today’s Security Digest