Skip to main content

Boteraser | Website and Server Security Solutions

🛡️ CVE-2026-23986 — copier

🟠 CVSS 7.1 — High ⚠️ Exploit Public CWE-61 OSV
7.1
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

Copier safe template has arbitrary filesystem write access via directory symlinks when _preserve_symlinks: true

Impact

Copier suggests that it's safe to generate a project from a safe template, i.e. one that doesn't use [unsafe](https://copier.readthedocs.io/en/stable/configuring/#unsafe) features like custom Jinja extensions which would require passing the --UNSAFE,--trust flag. As it turns out, a safe template can currently write to arbitrary directories outside the destination path by using directory a symlink along with [_preserve_symlinks: true](https://copier.readthedocs.io/en/stable/configuring/#preserve_symlinks) and a [generated directory structure](https://copier.readthedocs.io/en/stable/configuring/#generating-a-directory-structure) whose rendered path is inside the symlinked directory. This way, a malicious template author can create a template that overwrites arbitrary files (according to the user's write permissions), e.g., to cause havoc.

> [!NOTE]

>

> At the time of writing, the exploit is non-deterministic, as Copier walks the template's file tree using [os.scandir](https://docs.python.org/3/library/os.html#os.scandir) which yields directory entries in arbitrary order.

Reproducible example (may or may not work depending on directory entry yield order):

```shell

mkdir other/

pushd other/

echo "sensitive" > sensitive.txt

popd

mkdir src/

pushd src/

ln -s ../other other

echo "overwritten" > "{{ pathjoin('other', 'sensitive.txt') }}.jinja"

echo "_preserve_symlinks: true" > copier.yml

tree .

# .

# ├── copier.yml

# ├── other -> ../other

# └── {{ pathjoin('other', 'sensitive.txt') }}.jinja

#

# 1 directory, 2 files

popd

uvx copier copy --overwrite src/ dst/

cat other/sensitive.txt

# overwritten

```

Patches

n/a

Workarounds

n/a

References

n/a

How this vulnerability can be exploited

This issue can be reached with local access to the system, attack complexity is low, an attacker needs no privileges on the target. A user must be tricked into taking some action. Rated impact: confidentiality none, integrity high, availability high.

CVSS metrics in full

The score comes from this vector: CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:N/VI:H/VA:H/SC:N/SI:N/SA:N

  • Attack vector: Local — a local account, shell or session on the host is needed.
  • Attack complexity: Low — the attack works reliably, with no preparation.
  • Attack requirements: None — no deployment-specific condition has to hold.
  • Privileges required: None — an unauthenticated stranger can try it.
  • User interaction: Passive — a victim action is involved, but not a deliberate one.
  • Confidentiality impact: None.
  • Integrity impact: High — total loss, or loss the attacker controls.
  • Availability impact: High — total loss, or loss the attacker controls.

Weakness class

CVE-2026-23986 is classified as CWE-61: UNIX Symbolic Link (Symlink) Following. The product, when opening a file or directory, does not sufficiently account for when the file is a symbolic link that resolves to a target outside of the intended control sphere.

Affected software

CVE-2026-23986 is recorded against 1 package.

  • copier (fixed in 9.11.2)

Timeline and source

Published on 21 January 2026 and last revised on 7 July 2026. A public exploit is known to exist, which raises the urgency of patching considerably. A vendor advisory or fix has been published. Record sourced from OSV.

References

github.com (Web)
nvd.nist.gov (Advisory)
github.com (Web)
github.com (Package)
github.com (Web)

Other advisories for this package

copier has other advisories on record. If you are patching this one, these are worth checking on the same host:

Same weakness in other software

These advisories are the same class of weakness (CWE-61: UNIX Symbolic Link (Symlink) Following) in other software:

Details

Severity HIGH
CVSS Score 7.1
CVSS Vector CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:N/VI:H/VA:H/SC:N/SI:N/SA:N
CWE CWE-61
Public Exploit ⚠️ Yes
Source OSV
Published 2026-01-21
Updated 2026-08-20
Modified 2026-07-07

Affected Packages

Software From version Fixed in
copier — 9.11.2

Similar Threats

Exploit Protection

Are you running copier?

CVE-2026-23986 carries CVSS 7.1 High rating and a public exploit already exists. BotEraser checks your installation against this and other known CVE records, and blocks IPs associated with exploit activity.

Check My Site For CVE-2026-23986 →

No credit card required  ·  Results in minutes

ⓘ Data Notice: The information presented above has been compiled from publicly available internet sources. Boteraser aggregates this data solely for informational purposes and does not independently classify, evaluate, or endorse any findings about the vulnerabilities listed. The accuracy and completeness of this information is the sole responsibility of the original publishers. Boteraser and its operators accept no liability for any decisions made based on this data.

Browse related advisories

All advisoriesCVECVE 2026
✓