HackSpeak/CVE-2026-66066

GitHubRepository PoCExploit

PoC files

3 files

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GitHub
Analysisdeepseek-v4-pro:cloud ·

Technical assessment

A Python 3.11+ tool that exploits CVE-2026-66066 in Rails Active Storage with libvips. It crafts a hybrid MATLAB/HDF5 file to achieve arbitrary file read via the HDF5 External File List mechanism, recovers SECRET_KEY_BASE from /proc/self/environ, and forges a signed variation to execute arbitrary commands on the target server. Includes scan, probe, and check modes.

Backdoor review

No backdoor observed in reviewed code

The supplied evidence consists of a README and a Python script (kr2s.py) that implement a PoC for CVE-2026-66066. The code exercises the documented arbitrary-file-read chain and conditional RCE escalation exactly as described in the CVE and README. No concealed backdoor, unrelated payload, credential exfiltration to an attacker-controlled destination, or persistence mechanism was observed. The script's behavior is limited to interacting with a user-supplied target to demonstrate the vulnerability.

ClassificationExploit
Model confidence98%
AuthenticationNot required
Languagespython
Target softwareRuby on Rails Active Storagelibvips
Attack typesarbitrary file readremote code execution
Evidence & reasoningClassification basis · observed behavior · safety review
Technical evidence

Classification basis and observed behavior

Classification basis

The artifact contains code that actively exploits the vulnerability to achieve arbitrary file read and remote code execution. The 'rce' command recovers SECRET_KEY_BASE and executes attacker-supplied commands on the target. The 'check' and 'scan --active' commands upload malicious blobs to confirm the vulnerability. This goes beyond detection or scanning and constitutes an exploit.

kr2s.py:752-821kr2s.py:612-640kr2s.py:1006-1061

Requirements

  • Target Rails application uses Active Storage with libvips variant processing and accepts image uploads from untrusted users.README.md:9
  • Target is running a vulnerable Rails version (< 7.2.3.2, >= 8.0 < 8.0.5.1, >= 8.1 < 8.1.3.1) and libvips >= 8.13.README.md:14-15

Observed behavior

  • Crafts a hybrid file with MATLAB 5.0 header and HDF5 structure containing an external file list pointing to an arbitrary server-side path.kr2s.py:104-151
  • Uploads the crafted file to the Rails direct upload endpoint, claiming a content_type of image/png.kr2s.py:435-486
  • Triggers variant processing, causing libvips to read the external file and embed its content into a generated PNG image.kr2s.py:492-537
  • Decodes the returned PNG to recover the arbitrary file content.kr2s.py:173-272
  • Reads /proc/self/environ to extract SECRET_KEY_BASE and other secrets.kr2s.py:666-738
  • Uses the recovered SECRET_KEY_BASE to forge a signed Active Storage variation containing Ruby code that executes an arbitrary shell command.kr2s.py:167-170kr2s.py:752-821
  • Includes a scan mode that can actively upload malicious blobs to confirm vulnerability on multiple targets.kr2s.py:1006-1061
Safety-review evidence

Behaviors behind the backdoor verdict

Observables

File Read Primitive
read_file() function crafts a hybrid MATLAB/HDF5 file to read arbitrary server-side files via Active Storage/libvips.This is the core of the documented CVE-2026-66066 exploit chain.kr2s.py:540-562
Rce Escalation
cmd_rce() recovers SECRET_KEY_BASE, forges a signed variation containing a Ruby command, and reads back the output.This matches the conditional RCE escalation described in the CVE and README.kr2s.py:752-821
Target Interaction
The script uploads crafted blobs and triggers variant processing on a user-supplied target URL.All network activity is directed at the target specified by the user; no external exfiltration is performed.kr2s.py:435-486kr2s.py:492-537
Review boundaries

What the analysis did not establish

  • One file (likely lab/Dockerfile or similar) was omitted from the packet due to text budget, but the two included files (README.md and kr2s.py) provide complete coverage of the tool's behavior and classification.
  • One file (lab/ directory content) was omitted from the text evidence and was not reviewed. The inventory reports it as 1062 bytes of unclassified content, but its absence does not affect the analysis of the main PoC script.
  • The review does not assess the safety or correctness of the exploit code; it only evaluates the presence of backdoor or deceptive behavior.
Model interpretation

This review is limited to the supplied PoC code and context. It does not assert that the code works or is safe to execute.

Linked vulnerabilities

1