Threats / SolarWinds / CVE-2021-35211
CVE-2021-35211
· EUVD no mirror located
· GCVE no mirror located
Verified 2026-08-04
SolarWinds Serv-U vulnerability
SolarWinds Serv-U contains a memory corruption vulnerability enabling remote code execution without authentication. Actively exploited in ransomware campaigns.
Verdict
Today item, not a backlog item.
Critical remote code execution in widely deployed file transfer software. Memory safety flaw allows unauthenticated attackers to execute arbitrary code, leading to full system compromise. High exploitation prevalence in ransomware operations.
CISA KEV Yes · 2021-11-035Ransomware use Flagged5EPSS 0.9116 (verify live)6Exploit Weaponized · public PoC7CVSS 93CISA SSVC Exploitation: active · Automatable: no · Impact: total4
01
Is it exploitable?
— the evidence, ranked above the scoreExploit available
Fully weaponized — public exploit code is cataloged for this vulnerability.We link the existence of the exploit; we do not host or redistribute payloads.
Reported exploitation
21 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 2021-11-03), flagged for known ransomware use.
Probability (EPSS)
EPSS 0.9116 — modeled likelihood of exploitation activity.EPSS is a daily-changing model output — open the source for today's value.
Severity / affected
CVSS 9 (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H) · Affected: SolarWinds, Serv-U. Confirm exact fixed builds in the vendor advisory.CVSS — CNA-assigned (CVE.org), version 3.1, set at disclosure.
Weakness (CWE)
Mapped to CWE-787 Out-of-bounds Write — 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 112 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 public proof-of-concept / detection template). Catalog entries: nuclei template. 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 scan for exposed Serv-U instances and identify vulnerable versions without requiring credentials.
Business
Attackers gain initial network access to organizations running unpatched Serv-U servers, bypassing perimeter controls.
2
Keys to the kingdom — privilege/identity takeover narrative 2
Attacker
I craft a malicious payload targeting the memory corruption flaw to achieve code execution on the target system.
Business
The compromised Serv-U server becomes a beachhead for lateral movement and data exfiltration within the organization.
3
Lateral reach — past segmentation narrative 3
Attacker
I deploy ransomware or additional malware through the compromised Serv-U instance to encrypt or steal sensitive data.
Business
Operations halt due to encryption, customer data is exposed, and ransom demands create financial and reputational damage.
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
Coverage & confidence
— what we know, and what we don’tEstablished (cited)
Coverage gaps — stated, not hidden
Disclosure & credit2
Catalogued by SolarWindsCNA
Credited with finding itSolarWinds would like to thank the Microsoft Threat Intelligence Center (MSTIC) and Microsoft Offensive Security Researcunspecified