CVE-2021-3156

CVE-2021-3156 is a high-severity vulnerability in Sudo Project Sudo with a CVSS 3.x base score of 7.8. It is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, confirming it has been exploited in the wild (added 2022-04-06). The underlying weakness is classified as CWE-193.

Key facts

• Severity: High (CVSS 3.x base score 7.8)
• CVSS v2: 7.2
• EPSS exploit prediction: 99% (100th percentile)
• Actively exploited: Yes — listed in CISA KEV (added 2022-04-06)
• EU (EUVD) id: EUVD-2021-26500
• EU exploitation: Flagged exploited in the ENISA EU Vulnerability Database (since 2022-04-06)
• Weakness: CWE-193
• Affected product: Sudo Project Sudo
• Published: 2021-01-26
• Last modified: 2026-06-17

Description

Sudo before 1.9.5p2 contains an off-by-one error that can result in a heap-based buffer overflow, which allows privilege escalation to root via "sudoedit -s" and a command-line argument that ends with a single backslash character.

Frequently asked questions

What is CVE-2021-3156?

Sudo before 1.9.5p2 contains an off-by-one error that can result in a heap-based buffer overflow, which allows privilege escalation to root via "sudoedit -s" and a command-line argument that ends with a single backslash character.

How severe is CVE-2021-3156?

CVE-2021-3156 has a CVSS 3.x base score of 7.8, rated high severity. It is exploitable over local access with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2021-3156 being actively exploited?

Yes. CVE-2021-3156 is on CISA's Known Exploited Vulnerabilities (KEV) catalog, added on 2022-04-06, which means active exploitation has been confirmed. It should be prioritised for remediation.

What products are affected by CVE-2021-3156?

CVE-2021-3156 primarily affects Sudo Project Sudo. In total, 30 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-3156?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Because this CVE is known to be actively exploited, treat remediation as urgent — CISA KEV typically sets a short remediation deadline.

Does CVE-2021-3156 have an EU (EUVD) identifier?

Yes. CVE-2021-3156 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2021-26500. It is also flagged as exploited in the EUVD (since 2022-04-06).

When was CVE-2021-3156 published?

CVE-2021-3156 was published on 2021-01-26 and last updated on 2026-06-17.

References

• http://packetstormsecurity.com/files/161160/Sudo-Heap-Based-Buffer-Overflow.html
• http://packetstormsecurity.com/files/161230/Sudo-Buffer-Overflow-Privilege-Escalation.html
• http://packetstormsecurity.com/files/161270/Sudo-1.9.5p1-Buffer-Overflow-Privilege-Escalation.html
• http://packetstormsecurity.com/files/161293/Sudo-1.8.31p2-1.9.5p1-Buffer-Overflow.html
• http://packetstormsecurity.com/files/176932/glibc-syslog-Heap-Based-Buffer-Overflow.html
• http://seclists.org/fulldisclosure/2021/Feb/42
• http://seclists.org/fulldisclosure/2021/Jan/79
• http://seclists.org/fulldisclosure/2024/Feb/3
• http://www.openwall.com/lists/oss-security/2021/01/26/3
• http://www.openwall.com/lists/oss-security/2021/01/27/1
• http://www.openwall.com/lists/oss-security/2021/01/27/2
• http://www.openwall.com/lists/oss-security/2021/02/15/1
• http://www.openwall.com/lists/oss-security/2021/09/14/2
• http://www.openwall.com/lists/oss-security/2024/01/30/6
• http://www.openwall.com/lists/oss-security/2024/01/30/8
• https://kc.mcafee.com/corporate/index?page=content&id=SB10348
• https://lists.debian.org/debian-lts-announce/2021/01/msg00022.html
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/CALA5FTXIQBRRYUA2ZQNJXB6OQMAXEII/
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/LHXK6ICO5AYLGFK2TAX5MZKUXTUKWOJY/
• https://security.gentoo.org/glsa/202101-33
• https://security.netapp.com/advisory/ntap-20210128-0001/
• https://security.netapp.com/advisory/ntap-20210128-0002/
• https://support.apple.com/kb/HT212177
• https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-sudo-privesc-jan2021-qnYQfcM
• https://www.beyondtrust.com/blog/entry/security-advisory-privilege-management-for-unix-linux-pmul-basic-and-privilege-management-for-mac-pmm-affected-by-sudo-vulnerability
• https://www.debian.org/security/2021/dsa-4839
• https://www.kb.cert.org/vuls/id/794544
• https://www.openwall.com/lists/oss-security/2021/01/26/3
• https://www.oracle.com//security-alerts/cpujul2021.html
• https://www.oracle.com/security-alerts/cpuapr2022.html

Affected products (30)

• cpe:2.3:a:sudo_project:sudo:*:*:*:*:*:*:*:*
• cpe:2.3:a:sudo_project:sudo:1.9.5:-:*:*:*:*:*:*
• cpe:2.3:a:sudo_project:sudo:1.9.5:patch1:*:*:*:*:*:*
• cpe:2.3:o:fedoraproject:fedora:32:*:*:*:*:*:*:*
• cpe:2.3:o:fedoraproject:fedora:33:*:*:*:*:*:*:*
• cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:*
• cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:*
• cpe:2.3:a:netapp:active_iq_unified_manager:-:*:*:*:*:vmware_vsphere:*:*
• cpe:2.3:a:netapp:cloud_backup:-:*:*:*:*:*:*:*
• cpe:2.3:a:netapp:hci_management_node:-:*:*:*:*:*:*:*
• cpe:2.3:a:netapp:oncommand_unified_manager_core_package:-:*:*:*:*:*:*:*
• cpe:2.3:a:netapp:ontap_select_deploy_administration_utility:-:*:*:*:*:*:*:*
• cpe:2.3:a:netapp:ontap_tools:9:*:*:*:*:vmware_vsphere:*:*
• cpe:2.3:a:netapp:solidfire:-:*:*:*:*:*:*:*
• cpe:2.3:a:mcafee:web_gateway:8.2.17:*:*:*:*:*:*:*
• cpe:2.3:a:mcafee:web_gateway:9.2.8:*:*:*:*:*:*:*
• cpe:2.3:a:mcafee:web_gateway:10.0.4:*:*:*:*:*:*:*
• cpe:2.3:a:synology:diskstation_manager_unified_controller:3.0:*:*:*:*:*:*:*
• cpe:2.3:o:synology:diskstation_manager:6.2:*:*:*:*:*:*:*
• cpe:2.3:o:synology:skynas_firmware:-:*:*:*:*:*:*:*
• cpe:2.3:o:synology:vs960hd_firmware:-:*:*:*:*:*:*:*
• cpe:2.3:a:beyondtrust:privilege_management_for_mac:*:*:*:*:*:*:*:*
• cpe:2.3:a:beyondtrust:privilege_management_for_unix\/linux:*:*:*:*:basic:*:*:*
• cpe:2.3:o:oracle:micros_compact_workstation_3_firmware:310:*:*:*:*:*:*:*
• cpe:2.3:o:oracle:micros_es400_firmware:*:*:*:*:*:*:*:*
• cpe:2.3:o:oracle:micros_kitchen_display_system_firmware:210:*:*:*:*:*:*:*
• cpe:2.3:o:oracle:micros_workstation_5a_firmware:5a:*:*:*:*:*:*:*
• cpe:2.3:o:oracle:micros_workstation_6_firmware:*:*:*:*:*:*:*:*
• cpe:2.3:a:oracle:communications_performance_intelligence_center:*:*:*:*:*:*:*:*
• cpe:2.3:a:oracle:tekelec_platform_distribution:*:*:*:*:*:*:*:*

More vulnerabilities in Sudo Project Sudo

• CVE-2025-32463 — Critical (CVSS 9.3): Sudo before 1.9.17p1 allows local users to obtain root access because /etc/nsswitch.conf from a user-controlled…
• CVE-2019-14287 — High (CVSS 8.8): In Sudo before 1.8.28, an attacker with access to a Runas ALL sudoer account can bypass certain policy blacklists and…
• CVE-2017-1000368 — High (CVSS 8.2): Todd Miller's sudo version 1.8.20p1 and earlier is vulnerable to an input validation (embedded newlines) in the…
• CVE-2023-22809 — High (CVSS 7.8): In Sudo before 1.9.12p2, the sudoedit (aka -e) feature mishandles extra arguments passed in the user-provided…
• CVE-2021-23240 — High (CVSS 7.8): selinux_edit_copy_tfiles in sudoedit in Sudo before 1.9.5 allows a local unprivileged user to gain file ownership and…
• CVE-2019-18634 — High (CVSS 7.8): In Sudo before 1.8.26, if pwfeedback is enabled in /etc/sudoers, users can trigger a stack-based buffer overflow in the…

All CVEs affecting Sudo Project Sudo →

Other CWE-193 (Off-by-one Error) vulnerabilities

• CVE-2024-10442 — Critical (CVSS 10.0): Off-by-one error vulnerability in the transmission component in Synology Replication Service before 1.0.12-0066,…
• CVE-2026-53309 — Critical (CVSS 9.8): In the Linux kernel, the following vulnerability has been resolved: ocfs2/dlm: fix off-by-one in dlm_match_regions()…
• CVE-2024-38441 — Critical (CVSS 9.8): Netatalk before 3.2.1 has an off-by-one error and resultant heap-based buffer overflow because of setting ibuf[len] to…
• CVE-2023-46853 — Critical (CVSS 9.8): In Memcached before 1.6.22, an off-by-one error exists when processing proxy requests in proxy mode, if \n is used…
• CVE-2023-38429 — Critical (CVSS 9.8): An issue was discovered in the Linux kernel before 6.3.4. fs/ksmbd/connection.c in ksmbd has an off-by-one error in…
• CVE-2022-34970 — Critical (CVSS 9.8): Crow before 1.0+4 has a heap-based buffer overflow via the function qs_parse in query_string.h. On successful…

Browse all CWE-193 (Off-by-one Error) vulnerabilities →