SOC status:Duty analyst on shift

UK Cyber Defence
VulnerabilityModified

CVE-2018-10903

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.

HIGH 7.5EPSS 3.20%

Does this matter?

High impact if exploited, but EPSS currently rates exploitation as unlikely (3.20%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.

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.

CVSS 3.0
7.5 HIGHCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
EPSS
3.20% probability · 88th percentile
Public exploits
None in Exploit-DB
CISA KEV
Not listed
Weakness
CWE-20
Affected
cryptography/python-cryptography · redhat/openstack · canonical/ubuntu linux
Source
secalert@redhat.com
EPSS trend
0%3%5%27 October 2026: 3.20%27 October 202627 October 2026

EPSS 3.2% since 27 October 2026; no change recorded yet. Points are recorded when the score first appears and whenever it moves by a percentage point or more.

References

Source: NVD record, EPSS from FIRST.org, KEV from CISA, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.