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Medium, CVSS 6.6amended

python-dotenv: Symlink following in set_key allows arbitrary file overwrite via cross-device rename fallback

CVE-2026-28684GHSA-mf9w-mj56-hr94

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (python-dotenv 1.2.2), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
6.6 · CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:U/C:N/I:H/A:H
EPSS
  • CVE-2026-28684: 0.25% estimated exploitation activity in the next 30 days; percentile 16.80 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Summary setkey() and unsetkey() in python-dotenv follow symbolic links when rewriting .env files, allowing a local attacker to overwrite arbitrary files via a crafted symlink when a cross-device rename fallback is triggered. Details The rewrite() context manager in dotenv/main.py is used by both setkey() and unsetkey() to safely modify .env files. It works by writing to a temporary file (created in the system's default temp directory, typically /tmp) and then using shutil.move() to replace the original file. When the .env path is a symbolic link and the temp directory resides on a different filesystem than the target (a common configuration on Linux systems using tmpfs for /tmp), the following sequence occurs: 1. shutil.move() first attempts os.rename(), which fails with an OSError because atomic renames cannot cross device boundaries. 2. On failure, shutil.move() falls back to shutil.copy2() followed by os.unlink(). 3. shutil.copy2() calls shutil.copyfile() with followsymlinks=True…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 2 · amended ·

    Amended from ghsa record GHSA-mf9w-mj56-hr94

  2. Revision 1 · created ·

    Published from osv record GHSA-mf9w-mj56-hr94

Agent brief

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# Patch Next advisory brief: CVE-2026-28684

Advisory: python-dotenv: Symlink following in set_key allows arbitrary file overwrite via cross-device rename fallback
IDs: CVE-2026-28684, GHSA-mf9w-mj56-hr94
Record: https://patchnext.com/advisories/cve-2026-28684 (revision 2, source checked 26 Oct 2026, 13:40 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.6)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: python-dotenv 1.2.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI python-dotenv: affected < 1.2.2; fixed in 1.2.2

## Suggested inspection (read-only)
- `python -m pip show python-dotenv`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on python-dotenv.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-mf9w-mj56-hr94 (OSV record GHSA-mf9w-mj56-hr94 lists affected ranges: PyPI python-dotenv >=0 <1.2.2 (fixed))
- Verified: https://github.com/advisories/GHSA-mf9w-mj56-hr94 (GitHub-reviewed advisory GHSA-mf9w-mj56-hr94 lists affected ranges: PyPI python-dotenv >=0 <1.2.2)

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