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

Severity: medium (CVSS 5.4 v4.0)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.1% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-10-30 · updated 2026-10-30
Weakness: CWE-377

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.

Affected products

elixir-lang elixir: from 1.20.0-rc.4 before 1.20.5 — fixed in 1.20.5

How to fix

Upgrade to a fixed version: elixir-lang elixir 1.20.5. Check the vendor advisory for mitigations.

References

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