# CVE-2018-10903: PyCA Cryptography vulnerable to GCM tag forgery

Source: https://junglewise.ai/threats/cve-2018-10903-pyca-cryptography-vulnerable-to-gcm-tag-forgery  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2018-07-30  
License: CC BY 4.0 with a link back

CVE-2018-10903 · Severity: low · CVSS 3 · Published 2018-07-30

A flaw was found in python-cryptography versions between >=1.9.0 and <2.3. The finalize_with_tag API did not enforce a minimum tag length. If a user did not validate the input length prior to passing it to finalize_with_tag an attacker could craft an invalid payload with a shortened tag (e.g. 1 byte) such that they would have a 1 in 256 chance of passing the MAC check. GCM tag forgeries can cause key leakage.

Technologies: [cryptography (PyPI)](https://junglewise.ai/threats/technologies/cryptography). Vendors: [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is CVE-2018-10903 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2018-10903 being exploited in the wild.

**How severe is CVE-2018-10903?** Low severity, with a CVSS score of 3, published 30 July 2018.

**Which products and versions are affected?** cryptography (PyPI) ECOSYSTEM:introduced=1.9,fixed=2.3, ECOSYSTEM:introduced=1.9.0,fixed=2.3.

**Is there a fix for CVE-2018-10903?** Yes. cryptography (PyPI): upgrade to 2.3 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**Am I affected by CVE-2018-10903?** Check whether you run cryptography (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- cryptography (PyPI): upgrade to 2.3 or later

  ```sh
  pip install "cryptography>=2.3"
  ```


## Affected products

- cryptography (PyPI) ECOSYSTEM:introduced=1.9,fixed=2.3, ECOSYSTEM:introduced=1.9.0,fixed=2.3

## Identifiers

- CVE-2018-10903
- GHSA-fcf9-3qw3-gxmj
- PYSEC-2018-52

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