CVE-2018-10903

Publication date 20 July 2018

Last updated 25 August 2025

Ubuntu priority

Cvss 3 Severity Score

Description

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.

Read the notes from the security team

Status

Show unmaintained releases

Package	Ubuntu Release	Status
python-cryptography	18.04 LTS bionic	Fixed 2.1.4-1ubuntu1.2
	17.10 artful	Ignored end of life
	16.04 LTS xenial	Not affected
	14.04 LTS trusty	Not in release

Notes

leosilva

following what debian says, our xenial version is not affected.

Patch details

For informational purposes only. We recommend not to cherry-pick updates. How can I get the fixes?

Package	Patch details
python-cryptography	Upstream: https://github.com/pyca/cryptography/pull/4342/commits/688e0f673bfbf43fa898994326c6877f00ab19ef

Severity score breakdown

Parameter	Value
Base score	7.5 · High
Attack vector	Network
Attack complexity	Low
Privileges required	None
User interaction	None
Scope	Unchanged
Confidentiality	High
Integrity impact	None
Availability impact	None
Vector	CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N