CVE-2021-43837 Template injection in vault-cli
Attackers can execute arbitrary code via Jinja2 template injection in vault-cli if they control secret values, requiring an upgrade or disabling rendering.
- Exploited in the wild
- Not known
- Login needed
- An administrator
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2021-43837?
CVE-2021-43837 is a high-severity code injection vulnerability in peopledoc vault-cli, published on 16 Dec 2021. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
vault-cli is a configurable command-line interface tool (and python library) to interact with Hashicorp Vault. In versions before 3.0.0 vault-cli features the ability for rendering templated values. 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 is 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. In 3.0.0, the code related to interpreting vault templated secrets has been removed entirely. Users are advised to upgrade as soon as possible. For users unable to upgrade a workaround does exist. 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.
Which versions are affected by CVE-2021-43837?
3 open source packages ship an affected version, including vault-cli. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
vault-cli PyPI | All versions | 3.0.0 |
vault-cli PyPI | From 0.7.0 | 3.0.0 |
vault-cli PyPI | From 0.7.0 | 3.0.0 |
Products include Vault-Cli Project Vault-Cli.
How do I fix CVE-2021-43837?
Upgrade vault-cli to 3.0.0 or later.
Upgrade, and never evaluate templates, expressions or code built from user input. More about Code injection.
Is CVE-2021-43837 being exploited?
There is no known exploitation of CVE-2021-43837 in the wild and no public exploit code.
Sources
Also known as GHSA-q34h-97wf-8r8j, PYSEC-2021-853.