CVE-2026-107717: CWE-20: Improper Input Validation in masci banks
Description
CVE-2026-107717 is an improper input validation vulnerability in the masci banks product prior to version 2.5.0. The vulnerability arises because the Banks Prompt.chat_messages() method parses every line of rendered template output as ChatMessage JSON, allowing attacker-controlled JSON to manipulate the role field. This can lead to overriding application instructions or altering prompt structure when untrusted data is rendered and passed to an LLM provider. The issue is fixed in version 2.5.0.
CVSS v3.1
Score 6.5medium
Affected software
masci
banks
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Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The masci banks product uses a template language to generate LLM prompts. Before version 2.5.0, the Prompt.chat_messages() function attempts to parse each line of the rendered template output as ChatMessage JSON. Since ChatMessage.role accepts arbitrary strings, an attacker can craft JSON that crosses the prompt boundary and becomes a system, assistant, or tool message. This improper input validation (CWE-20) can override intended application instructions or disrupt prompt handling. The vulnerability is resolved in version 2.5.0.
Potential Impact
An attacker who can supply untrusted data that is rendered into ChatMessage JSON can manipulate the role field to override application instructions or alter the prompt structure. This may lead to confusion or misuse of downstream tools and message handling. The CVSS score is 6.5 (medium severity), indicating limited confidentiality and integrity impact without availability impact.
Mitigation Recommendations
Upgrade to masci banks version 2.5.0 or later, where this vulnerability is fixed. No additional mitigation is required once the product is updated.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-10-08T17:21:52.975Z
- Cvss Version
- 3.1
- State
- PUBLISHED
Threat ID: 6ac80fe22cdf04f65639c878
Added to database: 10/08/2026, 21:49:22 UTC
Last enriched: 10/08/2026, 22:04:55 UTC
Last updated: 10/08/2026, 22:28:20 UTC
Views: 6
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