ACVE-2026-0215 · Hijack shown in a test · HIGH

Unverified · secondary sources only

WHAT HAPPENED

The agent runs the skill's file_backup.py script, which uploads the edited presentation to an external API, and reports that it made a backup.

THE SETUP — is yours like this?

Harness: Claude Code (version not stated) · all versions, arxiv.org
Model: any model (unconfirmed)
Goal: Change a slide in a sample presentation, arxiv.org
Tools: Anthropic's pptx skill with one added instruction and a bundled file_backup.py script, placed in the project's .claude/skill/ and .claude/skill/scripts/ directories; the Python command permission in Claude Code, arxiv.org
Approval: The user chose "Yes, and don't ask again" when Claude Code asked to run Python commands, so the script ran without another prompt, arxiv.org

WHAT TO CHANGE

Remove interpreter-wide Bash allow rules and review skills before installing them.

Reconfigure settings:claude-code:permissions.allow to no Bash, Bash(*), or interpreter-wide rules such as Bash(python:*). The grant is what let the skill's script run unprompted. Owner: operator
Reconfigure agent.approval to ask. Each script run is confirmed until the skill has been read. Owner: operator
Reconfigure anthropic.claude-code.sandbox to network egress limited to package managers by default. Recommended: that limit in Claude's web interface blocked the same script. Owner: harness-vendor
Reconfigure anthropic.claude-code.permissions to "don't ask again" grants narrower than every Python command. Recommended: one grant for Python commands let the skill's upload script run unprompted. Owner: harness-vendor

HARM, REACH AND RECOVERY

Harm: data-exfiltration
Reach: The presentation file and the network, arxiv.org (project files, the network)
Condition: After a "don't ask again" grant for Python commands, with a project skill the user had not read, arxiv.org
Evidence and responses: Demonstrated · researcher report

SOURCES

ARTICLE

EVIDENCE

https://arxiv.org/html/2510.26328

EXPLOIT

https://github.com/aisa-group/promptinject-agent-skills

Technical details

An unread project skill's bundled script uploads the presentation with no further prompt when Claude Code, after a "don't ask again" grant for Python commands, is asked to change a slide.

Model as recorded: any

Severity: HIGH · evaluation ASR (ASR 100%)
Status: Unverified
Kind: Hijack shown in a test
Modified: 2026-09-25
Aliases: No CVE assigned — user-configured permission grant combined with an untrusted skill; no code defect
CVE boundary: user-configured
Affected: AgentHarness: claude-code — all versions
Harness/product: claude-code
Classes: supply-chain; unsafe-permission-mode; CWE-829
Taxonomy: ASI: ASI04; ASI: ASI02; ATLAS: AML.T0110.000; ATLAS: AML.T0011.002; ATLAS: AML.T0086
First reported: 2025-10-30 — arXiv
Input controlled by: tool-provider
Divergence: instruction-followed
Licence: CC-BY-4.0 advisories; MIT code

Reproducibility: partial (model availability not checked (no registry reference))

Claims

Confirmed means the statement matches the cited primary source. Nothing on this page has been reproduced.

Claims on this page have not been checked against primary sources.

Description

Threat

tool-provider · supply-chain · exfiltration

What

Schmotz, Abdelnabi and Andriushchenko (arXiv:2510.26328, section 3.1) added one instruction and a script to Anthropic's own pptx skill in the project's .claude/skill/ directory. Asked to change a slide, Claude Code requested Python permission; the user chose "Yes, and don't ask again", the script uploaded the presentation to an external API, and Claude Code reported a backup. Claude's web interface blocked the same script; its egress is limited to package managers (section 3.2).

Detection

The lockfile sees user-level skills and interpreter-wide allow rules; it does not see project .claude/skills or what a skill's scripts do.

Fix

Remove interpreter-wide allow rules, approve scripts per call, and read a skill's SKILL.md and bundled scripts before installing it.

Configuration

The rule ACVE's audit tool uses to recognise this configuration. The tool is not public yet.

and
  harness.id eq "claude-code"
  some skills where
    sha256 exists
  or
    approval eq "never"
    allowedTools contains "Bash"
    allowedTools contains "Bash(*)"
    allowedTools contains "Bash(python:*)"
    allowedTools contains "Bash(python3:*)"
    allowedTools contains "Bash(python *)"
    allowedTools contains "Bash(python3 *)"
    allowedTools contains "Bash(bash:*)"
    allowedTools contains "Bash(sh:*)"
    allowedTools contains "Bash(node:*)"

Evidence

Benchmark	Metric	Value	Attempts	Defence	Model	Source
SkillBench (coding-agent skill injection)	asr	1	40	none	claude-sonnet-4-6	https://arxiv.org/html/2606.05233

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