CVE-2018-10903: A flaw was found in python-cryptography versions between >=1.9.0 and <2.3

Q: How urgent is CVE-2018-10903?

Priority 58/100. High severity; Remotely exploitable, no login, no user action; On your watchlist

This month

HIGH 7.5REMOTEWATCHLISTUPGRADEDOWNGRADEMITIGATE

CVE-2018-10903 is a high-severity flaw (CVSS 7.5) affecting python-cryptography, openstack, ubuntu linux. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

High severity
Remotely exploitable, no login, no user action
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	3.2% (top 12%)
CISA exploited list	No
Weakness	CWE-20
Published	2018-07-30
Last modified	2026-06-17

Publisher (CNA): Red Hat, Inc. · Vendor: canonical · cryptography · redhat

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2018-07-30 16:29 UTCPublished CVE record published
2026-06-17 01:34 UTCUpdated Record last modified

cryptography python-cryptography UPGRADE

Affected: >= 1.9.0 and < 2.3

Fixed in: 2.3

Safe to downgrade to: a release before 1.9.0

1. Check installed version

apt-cache policy python-cryptography || rpm -q python-cryptography || python-cryptography --version

2. UPGRADE to 2.3 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade python-cryptography

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade python-cryptography

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 1.9.0 (Debian / Ubuntu)

apt-cache madison python-cryptography sudo apt install python-cryptography=<VERSION_BEFORE_1.9.0> sudo apt-mark hold python-cryptography

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list python-cryptography sudo dnf downgrade python-cryptography-<VERSION_BEFORE_1.9.0> sudo dnf versionlock add python-cryptography

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

redhat openstack DOWNGRADE

Affected: 13

Fixed in: no fixed release known

Safe to downgrade to: a release before 13

1. Check installed version

apt-cache policy openstack || rpm -q openstack || openstack --version

2. No fixed release: DOWNGRADE to a release before 13 (Debian / Ubuntu)

apt-cache madison openstack sudo apt install openstack=<VERSION_BEFORE_13> sudo apt-mark hold openstack

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list openstack sudo dnf downgrade openstack-<VERSION_BEFORE_13> sudo dnf versionlock add openstack

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

canonical ubuntu linux MITIGATE

Affected: 18.04

Fixed in: no fixed release known

Safe to downgrade to: a release before 18.04

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2018-10903?

python-cryptography: upgrade to 2.3; openstack: downgrade or apply the listed mitigation; ubuntu linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2018-10903 being exploited?

CVE-2018-10903 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2018-10903 affect?

CVE-2018-10903 affects python-cryptography, openstack, ubuntu linux. Severity is high (CVSS 7.5). 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 coul

How urgent is CVE-2018-10903?

Priority 58/100. High severity; Remotely exploitable, no login, no user action; On your watchlist

Software pages

Python vulnerabilities · Ubuntu vulnerabilities · OpenStack vulnerabilities

References

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