Threats / Sudo / CVE-2021-3156
CVE-2021-3156
· EUVD no mirror located
· GCVE no mirror located
Verified 2026-08-04
Sudo vulnerability
Sudo contains an off-by-one error causing heap-based buffer overflow, enabling privilege escalation on affected systems.
Verdict
Today item — known-exploited.
A memory corruption flaw in Sudo's argument parsing allows unauthenticated or low-privileged attackers to overflow heap buffers and gain root access. Active exploitation in the wild with high EPSS score indicates immediate risk to unpatched deployments.
CISA KEV Yes · 2022-04-064EPSS 0.99295 (verify live)5Exploit Public PoC6CVSS 7.8 (CISA)3CISA SSVC Exploitation: active · Automatable: no · Impact: total3
01
Is it exploitable?
— the evidence, ranked above the scoreExploit available
Public proof-of-concept exploit code is cataloged for this vulnerability.We link the existence of the exploit; we do not host or redistribute payloads.
Reported exploitation
8 independent public reports of in-the-wild exploitation are cataloged.Distinct reporting sources (vendor, incident response, government); open them for the underlying claims.
Exploited in the wild
Listed in the CISA Known Exploited Vulnerabilities catalog (added 2022-04-06).
Probability (EPSS)
EPSS 0.99295 — modeled likelihood of exploitation activity.EPSS is a daily-changing model output — open the source for today's value.
Severity / affected
CVSS 7.8 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H) · Affected: Sudo, Sudo. Confirm exact fixed builds in the vendor advisory.CVSS — CISA-assigned via the ADP container (CVE.org), version 3.1; the CNA left no metrics, so CISA's own score is used ahead of NVD.
Weakness (CWE)
Mapped to CWE-122 Heap-based Buffer Overflow, CWE-193 CWE-193 — weakness family: Memory safety.CWE assignment from the public NVD record (may be stale); the weakness class drives how the flaw is exploited.
CISA SSVC (triage disposition)
Exploitation: active · Automatable: no · Technical Impact: totalCISA's own stakeholder-specific triage inputs, published in the CVE record (CISA Coordinator role). NOTE: this is CISA's three decision points; the final Act/Attend/Track decision also requires a Mission & Well-being input not published here, so no overall decision is asserted.
Currency of the record
CISA added this to its KEV catalog 435 days after the CVE record was published.KEV lag = CISA-KEV dateAdded − CVE.org datePublished; a floor on how long the known-exploited flaw sat in the public record before the federal catalog listed it. Severity/weakness here is CNA- or CISA-assigned (current at disclosure), independent of NVD's analysis backlog.
Public exploit available
Public exploit tooling is catalogued for this CVE (a functional/weaponized public exploit). Catalog entries: Metasploit module. We link the catalog page(s) only — no payload or code is hosted or restated here.Link, never host — the catalog page is the source; basicsecurity.net does not redistribute payloads.
02
Who’s exploiting it?
— attribution turns risk into urgencyAttribution not established
No confirmed (advisory-backed) threat-actor attribution is established for this record. Absence of a named actor is not absence of compromise — see Coverage & confidence.
03
Why it matters
— the attack path, told twice: adversary, then board1
Front door — unauthenticated access narrative 1
Attacker
I craft a malicious command-line argument that triggers the off-by-one error in Sudo's buffer handling.
Business
An attacker gains unauthorized root-level access to critical infrastructure, enabling full system compromise.
2
Keys to the kingdom — privilege/identity takeover narrative 2
Attacker
I exploit the heap overflow to overwrite adjacent memory structures and redirect execution flow to my payload.
Business
Confidential data, intellectual property, and operational systems become accessible to the threat actor.
3
Lateral reach — past segmentation narrative 3
Attacker
I establish persistent access by installing backdoors or modifying system configurations with elevated privileges.
Business
Incident response costs, forensic investigation, and extended remediation efforts multiply across affected environments.
04
What to do
— defensible action- Remediate per the vendor advisory — confirm the fixed build for your version and verify exposure.1
Say it to the boardA vulnerability with this evidence profile is a defensible budget line, not a backlog ticket — fund the change against the proof above.
05