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Fencer Vulns
critical 10.0

CVE-2026-73299 json

Prompty: Server-Side Template Injection to Remote Code Execution in the @prompty/core Nunjucks Renderer

published 2026-07-24 3 mo ago modified 2026-10-24 15 d ago also GHSA-w28w-gp39-m4p6 , EUVD-2026-57382

cvss
10.0
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
1.8%
EPSS 1.8% chance of exploitation in 30 days, percentile 78%
public exploits
0
none known

Summary

Prompty is a markdown file format (.prompty) for LLM prompts. Prior to 0.1.5 and 2.0.0-beta.5, the TypeScript Nunjucks renderer evaluated untrusted .prompty template bodies with unrestricted JavaScript member access. An attacker-controlled template could traverse constructor and prototype properties to execute JavaScript in the host Node.js process. This issue is fixed in versions 0.1.5 and 2.0.0-beta.5.

Patch / fix

  • npm @prompty/core 0.1.5, 2.0.0-beta.5

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
total
Assessed
2 mo ago

Exploit prediction

1.78% chance of exploitation in the next 30 days, higher than 78% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 10.0 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
GitHub 3.1 10.0 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

Affected packages

ecosystem package affected fixed in
npm @prompty/core
<0.1.5
>=2.0.0-alpha.1, <2.0.0-beta.5
0.1.5
2.0.0-beta.5

Affected products

  • microsoft prompty

Classification

Weakness
  • CWE-94 Improper Control of Generation of Code
  • CWE-1336 Improper Neutralization of Special Elements Used in a Template Engine

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.