How severe is CVE-2021-31556?

CVE-2021-31556 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2021-31556 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (73rd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-31556?

CVE-2021-31556 primarily affects Mediawiki. In total, 4 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-31556?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

When was CVE-2021-31556 published?

CVE-2021-31556 was published on 2021-08-12 and last updated on 2026-06-17.

CVE-2021-31556

CVE-2021-31556 is a critical-severity vulnerability in Mediawiki with a CVSS 3.x base score of 9.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-1284.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
CVSS v2: 7.5
EPSS exploit prediction: 2% (73rd percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-1284
Affected product: Mediawiki
Published: 2021-08-12
Last modified: 2026-06-17

Description

An issue was discovered in the Oauth extension for MediaWiki through 1.35.2. MWOAuthConsumerSubmitControl.php does not ensure that the length of an RSA key will fit in a MySQL blob.

Frequently asked questions

What is CVE-2021-31556?: An issue was discovered in the Oauth extension for MediaWiki through 1.35.2. MWOAuthConsumerSubmitControl.php does not ensure that the length of an RSA key will fit in a MySQL blob.
How severe is CVE-2021-31556?: CVE-2021-31556 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-31556 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (73rd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-31556?: CVE-2021-31556 primarily affects Mediawiki. In total, 4 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-31556?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2021-31556 published?: CVE-2021-31556 was published on 2021-08-12 and last updated on 2026-06-17.

References

Affected products (4)

cpe:2.3:a:mediawiki:mediawiki:*:*:*:*:*:*:*:*
cpe:2.3:o:fedoraproject:fedora:33:*:*:*:*:*:*:*
cpe:2.3:o:fedoraproject:fedora:34:*:*:*:*:*:*:*
cpe:2.3:o:fedoraproject:fedora:35:*:*:*:*:*:*:*

More vulnerabilities in Mediawiki

CVE-2025-67484 — Critical (CVSS 9.8): Vulnerability in Wikimedia Foundation MediaWiki. This vulnerability is associated with program files…
CVE-2024-34502 — Critical (CVSS 9.8): An issue was discovered in WikibaseLexeme in MediaWiki before 1.39.6, 1.40.x before 1.40.2, and 1.41.x before 1.41.1.…
CVE-2023-37303 — Critical (CVSS 9.8): An issue was discovered in the CheckUser extension for MediaWiki through 1.39.3. In certain situations, an attempt to…
CVE-2023-29141 — Critical (CVSS 9.8): An issue was discovered in MediaWiki before 1.35.10, 1.36.x through 1.38.x before 1.38.6, and 1.39.x before 1.39.3. An…
CVE-2022-29906 — Critical (CVSS 9.8): The admin API module in the QuizGame extension for MediaWiki through 1.37.2 (before…
CVE-2022-29904 — Critical (CVSS 9.8): The SemanticDrilldown extension for MediaWiki through 1.37.2 (before e688bdba6434591b5dff689a45e4d53459954773) allows…

All CVEs affecting Mediawiki →

Other CWE-1284 (Improper Validation of Specified Quantity in Input) vulnerabilities

CVE-2026-49777 — Critical (CVSS 10.0): Improper Validation of Specified Quantity in Input vulnerability in ShapedPlugin, LLC Product Slider Pro for…
CVE-2024-8887 — Critical (CVSS 10.0): CIRCUTOR Q-SMT in its firmware version 1.0.4, could be affected by a denial of service (DoS) attack if an attacker with…
CVE-2022-20699 — Critical (CVSS 10.0): Multiple vulnerabilities in Cisco Small Business RV160, RV260, RV340, and RV345 Series Routers could allow an attacker…
CVE-2021-21960 — Critical (CVSS 10.0): A stack-based buffer overflow vulnerability exists in both the LLMNR functionality of Sealevel Systems, Inc. SeaConnect…
CVE-2021-21951 — Critical (CVSS 10.0): An out-of-bounds write vulnerability exists in the CMD_DEVICE_GET_SERVER_LIST_REQUEST functionality of the…
CVE-2021-21950 — Critical (CVSS 10.0): An out-of-bounds write vulnerability exists in the CMD_DEVICE_GET_SERVER_LIST_REQUEST functionality of the…

Browse all CWE-1284 (Improper Validation of Specified Quantity in Input) vulnerabilities →