CVE-2018-10903

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.

Published: 2018-07-30 Last update: 2026-06-16 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2018-10903 is rated Moderate Risk (60.9/100): CVSS High severity, with medium exploitation likelihood (EPSS 3.20%). Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2018-10903

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-07-07 2.60% 3.20% +0.59%
2 2026-06-15 0.21% 2.60% +2.39%
3 2025-11-21 — 0.21% —

Full EPSS history (12 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2018-10903

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.5 3.0 HIGH
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:N)
Service keeps running; no real outage angle.
 3.9 3.6 [email protected]
7.5 3.0 HIGH
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:N)
Service keeps running; no real outage angle.
 3.9 3.6 [email protected]
5.0 2.0 MEDIUM
AV:N/AC:L/Au:N/C:P/I:N/A:N Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:P)
Partial confidentiality impact.
Integrity impact (I:N)
No integrity impact.
Availability impact (A:N)
No availability impact.
 10.0 2.9 [email protected]

Weakness enumeration for CVE-2018-10903

GitHub Security Advisory for CVE-2018-10903

GHSA-fcf9-3qw3-gxmj · Severity: high · Ecosystem: pip — PyCA Cryptography vulnerable to GCM tag forgery

OS Trackers for CVE-2018-10903

vendor priority summary link
debian not yet assigned CVE-2018-10903 not yet assigned priority: Debian including 1 source packages (python-cryptography), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2018-10903
redhat medium — https://access.redhat.com/security/cve/CVE-2018-10903
suse high CVE-2018-10903 severity important: SUSE including 298 source package names (1.1.0-build4.19.12:python3-cryptography-2.9.2-150200.13.1, 1.10.1.16.4.5.328:python3-cryptography-2.9.2-150200.13.1, …), 529 product×package rows across 100 product lines (Container ses/7.1/cephcsi/cephcsi, Container ses/7.1/rook/ceph, … (100 product lines)): Fixed 310, Known Affected 219. https://www.suse.com/security/cve/CVE-2018-10903/
ubuntu medium CVE-2018-10903 medium priority: Ubuntu including 1 source packages (python-cryptography), 5 status rows across 5 suites (artful, bionic, trusty, upstream, xenial): DNE 1, ignored 1, needs-triage 1, not-affected 1, released 1. https://ubuntu.com/security/CVE-2018-10903

Affected software / configurations for CVE-2018-10903

Vendor Product Version Raw CPE
cryptography python-cryptography >= 1.9.0, < 2.3 cpe:2.3:a:cryptography:python-cryptography:*:*:*:*:*:*:*:*
redhat openstack 13 cpe:2.3:a:redhat:openstack:13:*:*:*:*:*:*:*
canonical ubuntu_linux 18.04 cpe:2.3:o:canonical:ubuntu_linux:18.04:*:*:*:lts:*:*:*

References for CVE-2018-10903

cvelogic Threat Intelligence