CVE-2026-77357

Mesop: DoS in /hot-reload endpoint allows unauthenticated attacker to exhaust worker threads and crash the server

Published Aug 25, 2026 CVSS 4.0 · 8.7 High EPSS < 1% KEV · Not listed

Description

Mesop is a Python-based UI framework that allows users to build web applications. Prior to 1.3.3, applications running in debug mode expose a GET /hot-reload endpoint whose unbounded loop depends on the user-supplied counter parameter, allowing an unauthenticated attacker to hold worker threads with high counter values until the worker pool is exhausted and the server becomes unavailable. A single unauthenticated attacker can crash the Mesop server with minimal effort. Because the attack leverages worker exhaustion, the server remains unresponsive until it is manually restarted. This issue is fixed in version 1.3.3.

Analysis

Technical impact

Mesop, a Python‑based UI framework, allowed an unauthenticated attacker to trigger a denial of service by sending a GET request to the /hot‑reload endpoint while the application ran in debug mode. The endpoint parsed a user‑supplied counter parameter that drove an unbounded loop, consuming worker threads until the worker pool was exhausted and the server became unresponsive. A single attacker could crash the server with minimal effort, and the server remained unavailable until manually restarted.

Affected Systems

The vulnerability affects the Mesop framework from the mesop‑dev vendor, specifically any deployment using a version earlier than 1.3.3 that is running in debug mode. Version 1.3.3 and later contain the fix.

Risk and Exploitability

With a CVSS score of 8.7, this is a high severity vulnerability. The attack vector is inferred to be an external HTTP GET to /hot‑reload, requiring no authentication. Because exploitation simply exhausts worker threads, the EPSS score is not available, and the vulnerability is not listed in CISA KEV. An attacker can achieve a full service outage, affecting availability for all users of the impacted server.

Affected Products

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions

mesop-dev

mesop

affected

Version	Status	Constraints
`< 1.3.3`	affected	—

No data.

Vendor Product Versions

Mesop-dev

Mesop

Version	Status	Scheme	Platform
`[0,1.3.3)`	affected	semver	—

Remediation

No solution or workaround provided in the CVE record.

OpenCVE Recommended Actions

Upgrade Mesop to version 1.3.3 or later.
Disable debug mode or completely remove the /hot-reload endpoint from production deployments.
Employ network‑level rate limiting or firewall rules to block abusive accesses to the /hot-reload endpoint.

Generated by OpenCVE AI on August 26, 2026 at 01:44 UTC.

Tracking

Advisories

No advisories available

Metrics

Attack Vector Network

Attack Complexity Low

Privileges Required None

Attack Requirements None

User Interaction None

Vulnerable System Confidentiality Impact None

Vulnerable System Integrity Impact None

Vulnerable System Availability Impact High

Subsequent System Confidentiality Impact None

Subsequent System Integrity Impact None

Subsequent System Availability Impact None

No CVSS v3.1

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

Exploit prediction score: < 1% (0.529% probability within 30 days)

Exploitation poc

Automatable yes

Technical Impact partial

References

Link	Providers
https://github.com/mesop-dev/mesop/commit/2b8e7f2c349c9e2eec202f46b07bada83061ce2d
https://github.com/mesop-dev/mesop/releases/tag/v1.3.3
https://github.com/mesop-dev/mesop/security/advisories/GHSA-8p72-497j-83mx

History

Aug 26, 2026 1:30 PM Scoring metrics updated View changes

Type	Values Removed	Values Added
Metrics		ssvc `{'options': {'Automatable': 'yes', 'Exploitation': 'poc', 'Technical Impact': 'partial'}, 'version': '2.0.3'}`

Aug 26, 2026 2:15 AM First appearance in the feed. Affected vendors updated View changes

Type	Values Removed	Values Added
First Time appeared		Mesop-dev Mesop-dev mesop
Vendors & Products		Mesop-dev Mesop-dev mesop

Aug 25, 2026 9:00 PM Description updated. Title updated. Weaknesses updated. Added references. Scoring metrics updated View changes

Type	Values Removed	Values Added
Description		Mesop is a Python-based UI framework that allows users to build web applications. Prior to 1.3.3, applications running in debug mode expose a GET /hot-reload endpoint whose unbounded loop depends on the user-supplied counter parameter, allowing an unauthenticated attacker to hold worker threads with high counter values until the worker pool is exhausted and the server becomes unavailable. A single unauthenticated attacker can crash the Mesop server with minimal effort. Because the attack leverages worker exhaustion, the server remains unresponsive until it is manually restarted. This issue is fixed in version 1.3.3.
Title		Mesop: DoS in /hot-reload endpoint allows unauthenticated attacker to exhaust worker threads and crash the server
Weaknesses		CWE-400 CWE-834
References		https://github.com/mesop-dev/mesop/commit/2b8e7f2c349c9e2eec202f46b07bada83061ce2d https://github.com/mesop-dev/mesop/releases/tag/v1.3.3 https://github.com/mesop-dev/mesop/security/advisories/GHSA-8p72-497j-83mx
Metrics		cvssV4_0 `{'score': 8.7, 'vector': 'CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N'}`