# CVE-2020-13757: PYSEC-2020-99 - Python-RSA before 4.1 ignores leading '\0' bytes during decryption of ciphertext. This could conceivably have a security-relevant impact, e.

Source: https://junglewise.ai/threats/cve-2020-13757-python-rsa-decryption-of-ciphertext-leads-to-dos  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2020-06-01  
License: CC BY 4.0 with a link back

CVE-2020-13757 · Severity: low · CVSS 3.1 · Published 2020-06-01

Python-RSA before 4.1 ignores leading '\0' bytes during decryption of ciphertext. This could conceivably have a security-relevant impact, e.g., by helping an attacker to infer that an application uses Python-RSA, or if the length of accepted ciphertext affects application behavior (such as by causing excessive memory allocation).

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

## Quick answers

**Is CVE-2020-13757 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2020-13757 being exploited in the wild.

**How severe is CVE-2020-13757?** Low severity, with a CVSS score of 3.1, published 1 June 2020.

**Which products and versions are affected?** rsa (PyPI) ECOSYSTEM:introduced=0,fixed=4.1.

**Is there a fix for CVE-2020-13757?** Yes. rsa (PyPI): upgrade to 4.1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**Am I affected by CVE-2020-13757?** Check whether you run rsa (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

- rsa (PyPI): upgrade to 4.1 or later

  ```sh
  pip install "rsa>=4.1"
  ```


## Affected products

- rsa (PyPI) ECOSYSTEM:introduced=0,fixed=4.1

## Identifiers

- CVE-2020-13757
- GHSA-537h-rv9q-vvph
- PYSEC-2020-99

## Related threats

- [Timing attacks in python-rsa](https://junglewise.ai/threats/cve-2020-25658-timing-attacks-in-python-rsa)
- [Python RSA allows attackers to spoof signatures](https://junglewise.ai/threats/cve-2016-1494-python-rsa-allows-attackers-to-spoof-signatures)