How severe is CVE-2021-43837?

CVE-2021-43837 has a CVSS score of 9.1/10, rated CRITICAL. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-43837?

CVE-2021-43837 affects the following packages: vault-cli (PyPI). Ecosystems affected: PyPI.

How do I fix CVE-2021-43837?

Update vault-cli to 3.0.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-43837 is resolved across your whole dependency graph.

How do I detect CVE-2021-43837 in my PyPI dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for vault-cli, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2021-43837 if there is no patch (or I can't update yet)?

Stop passing untrusted input into the interpreter or shell: call the affected binary with an argument array rather than a composed command string, reject anything outside a strict allowlist of expected values, and run the component under an account that cannot reach beyond the work it legitimately does.

Is CVE-2021-43837 actively exploited in the wild?

Yes. There are 2 known exploit references for CVE-2021-43837, including 2 in-the-wild exploitations observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

What is the EPSS score for CVE-2021-43837?

CVE-2021-43837 has an EPSS (Exploit Prediction Scoring System) score of 5.0%, placing it in the 92th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2021-43837?

CVE-2021-43837 is classified as CWE-74 (CWE-74), Code Injection (CWE-94). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

When was CVE-2021-43837 published, and has it been updated?

CVE-2021-43837 was published on December 16, 2021 and was last updated on July 9, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐍

🐍 PyPI

Not in CISA KEV

CRITICAL severity

CVE-2021-43837 — vault-cli

CRITICALFix: peopledoc/vault-cli@3ba3955

CVE-2021-43837 is a critical-severity (CVSS 9.1) CWE-74 vulnerability in vault-cli. 2 public exploit references exist, so weaponization risk is real. A fix is available for vault-cli — see the affected versions and patch details below.

vault-cli contains possible RCE when reading user-defined data

Also known asGHSA-q34h-97wf-8r8jPYSEC-2021-853

Published

Dec 16, 2021

Updated

Jul 9, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

2 known

Exploitation data as of Oct 6, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

5.0%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs92th percentile — riskier than 92% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2021-43837 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,738 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected

🐍vault-cli

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.

Description

Impact

What kind of vulnerability is it? Who is impacted?

vault-cli features the ability for rendering templated values (as explained in the documentation). When a secret starts with the prefix !template!, vault-cli interprets the rest of the contents of the secret as a Jinja2 template. Jinja2 is a powerful templating engine and it's not designed to safely render arbitrary templates. An attacker controlling a jinja2 template rendered on a machine can trigger arbitrary code, making this a Remote Code Execution (RCE) risk. If the content of the vault can be completely trusted, then this is not a problem. Otherwise, if your threat model includes cases where an attacker can manipulate a secret value read from the vault using vault-cli, then this vulnerability may impact you.

This does not impact vault itself, except for the fact that the attacker, having an RCE on the machine that executes vault-cli, may abuse the token that vault-cli uses, to read, write or delete other data from the vault.

Patches

Has the problem been patched? What versions should users upgrade to?

In 3.0.0, the code related to interpreting vault templated secrets has been removed entirely.

Workarounds

Is there a way for users to fix or remediate the vulnerability without upgrading?

Using the environment variable VAULT_CLI_RENDER=false or the flag --no-render (placed between vault-cli and the subcommand, e.g. vault-cli --no-render get-all) or adding render: false to the vault-cli configuration yaml file disables rendering and removes the vulnerability. Using the python library, you can use: vault_cli.get_client(render=False) when creating your client to get a client that will not render templated secrets and thus operates securely.

References

Are there any links users can visit to find out more?

Here's an article explaining how jinja2 templates might be exploited to have side effects: https://podalirius.net/en/publications/grehack-2021-optimizing-ssti-payloads-for-jinja2/

For more information

If you have any questions or comments about this advisory:

Open an issue in the vault-cli repo

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐍PyPI	`vault-cli`	≥ 0.7.0&&< 3.0.0	3.0.0`pip install --upgrade 'vault-cli==3.0.0'`

Affected Products

1 product · 1 configurations

Application

vault-clivault-cli_project

≥ 0.7.0 && < 3.0.0

range

Exploits & PoCs

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

vault-cli is a configurable command-line interface tool (and python libr…

podalirius.netNVDDec 2021

vault-cli is a configurable command-line interface tool (and python libr…

github.comNVDDec 2021

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for vault-cli, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update vault-cli to 3.0.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-43837 is resolved across your whole dependency graph.
Workarounds
Stop passing untrusted input into the interpreter or shell: call the affected binary with an argument array rather than a composed command string, reject anything outside a strict allowlist of expected values, and run the component under an account that cannot reach beyond the work it legitimately does.

Frequently Asked Questions

### Impact _What kind of vulnerability is it? Who is impacted?_ vault-cli features the ability for rendering templated values (as explained in the [documentation](https://github.com/peopledoc/vault-cli/blob/2.2.1/docs/howto/templated_secrets.rst)). When a secret starts with the prefix `!template!`, vault-cli interprets the rest of the contents of the secret as a Jinja2 template. Jinja2 is a powerful templating engine and it's not designed to safely render arbitrary templates. An attacker controlling a jinja2 template rendered on a machine can trigger arbitrary code, making this a Remote Code