CVE-2021-35211 (GCVE-0-2021-35211)
Vulnerability from cvelistv5 – Published: 2021-07-14 20:55 – Updated: 2025-10-21 23:25Title
Serv-U Remote Memory Escape Vulnerability
Summary
Microsoft discovered a remote code execution (RCE) vulnerability in the SolarWinds Serv-U product utilizing a Remote Memory Escape Vulnerability. If exploited, a threat actor may be able to gain privileged access to the machine hosting Serv-U Only. SolarWinds Serv-U Managed File Transfer and Serv-U Secure FTP for Windows before 15.2.3 HF2 are affected by this vulnerability.
Severity
9 (Critical)
SSVC
Exploitation: active
Automatable: no
Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2025-02-04 19:06 UTC
CWE
- Memory Escape Vulnerability in Solarwinds Serv-U
- CWE-787 - Out-of-bounds Write
Assigner
References
3 references
| URL | Tags |
|---|---|
| https://www.solarwinds.com/trust-center/security-… | x_refsource_MISC |
| https://www.microsoft.com/security/blog/2021/07/1… | x_refsource_MISC |
| https://www.cisa.gov/known-exploited-vulnerabilit… | government-resource |
Impacted products
1 product
| Vendor | Product | Version | CPE status | |
|---|---|---|---|---|
| SolarWinds | Serv-U Managed File Transfer Server and Serv-U Secured FTP |
Affected:
SolarWinds Serv-U , < 15.2.3 HF1
(custom)
|
guessed |
Date Public
2021-07-13 00:00
CISA
Known Exploited Vulnerability - GCVE BCP-07 Compliant
KEV entry ID: eb2b7865-a421-4559-b37e-aed4ee78c423
Exploited: Yes
Timestamps
First Seen: 2021-11-03
Asserted: 2021-11-03
Scope
Notes: SolarWinds Serv-U Remote Code Execution Vulnerability | Affected: SolarWinds / Serv-U | Description: SolarWinds Serv-U contains an unspecified memory escape vulnerability which can allow for remote code execution. | Required action: Apply updates per vendor instructions. | Due date: 2021-11-17 | Known ransomware campaign use (KEV): Known | Notes (KEV): https://nvd.nist.gov/vuln/detail/CVE-2021-35211
Evidence
Type: Vendor Report
Signal: Successful Exploitation
Confidence: 80%
Source: cisa-kev
Details
| Cwes | CWE-787 |
|---|---|
| Feed | CISA Known Exploited Vulnerabilities Catalog |
| Product | Serv-U |
| Due Date | 2021-11-17 |
| Date Added | 2021-11-03 |
| Vendorproject | SolarWinds |
| Vulnerabilityname | SolarWinds Serv-U Remote Code Execution Vulnerability |
| Knownransomwarecampaignuse | Known |
References
Created: 2026-02-02 12:29 UTC
| Updated: 2026-11-04 13:36 UTC
Previdian
Known Exploited Vulnerability - GCVE BCP-07 Compliant
KEV entry ID: cf622c5e-a0f9-46dd-a35a-2000979b5b0a
Exploited: Yes
Timestamps
First Seen: 2021-11-03
Asserted: 2021-11-03
Scope
Notes: KEVIntel entry: Serv-U Remote Memory Escape Vulnerability | Affected: SolarWinds / Serv-U Managed File Transfer Server and Serv-U Secured FTP | CVSS: 9.0 (CRITICAL) | Used in malware: yes | Not yet in CISA KEV: False
Evidence
Type: Public Report
Signal: Confirmed Compromise
Confidence: 70%
Source: kevintel
Details
| Feed | KEVIntel (kevintel.com) |
|---|---|
| Title | Serv-U Remote Memory Escape Vulnerability |
| Vendor | SolarWinds |
| Product | Serv-U Managed File Transfer Server and Serv-U Secured FTP |
| Added Date | 2021-11-03T00:00:00.000Z |
| Cvss Score | 9.0 |
| Epss Score | None |
| Cvss Severity | CRITICAL |
| Epss Percentile | None |
| Used In Malware | yes |
| Ahead Of Cisa Kev | None |
| Not Yet In Cisa Kev | False |
References
Created: 2026-06-23 14:04 UTC
| Updated: 2026-07-10 06:14 UTC
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Solutions
CNA · SolarWinds
SolarWinds has released a hotfix 15.2.3 HF2 It is suggested to upgrade to the latest hotfix as soon as possible
Workarounds
CNA · SolarWinds
SolarWinds advises to disconnect Serv-U Server from internet until patched.
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Drag nodes to arrange them. Double-click a related vulnerability to open it, or a source to visit its link. The Physics button on the left tunes the layout and the simulation; the legend at the bottom left hides or shows nodes by kind and by sighting type.
Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
Vulnerability timeline
Sightings and recorded dates, grouped by day · UTC
How durations are calculated
Following the VTEM framework (Black Hat USA 2015), time to patch starts when the vendor or a coordinator was informed, total time to patch at discovery, and disclosure to patch at public disclosure; vendor response time runs from the report to its acknowledgement. Time to exploit and time unpatched start at the earliest discovery or report, falling back to public disclosure. Unpatched time ends at the first recorded patch, or the calculation time when no patch is recorded. Exploitation to patch shows the interval between those two events; a published proof of concept is a public exploit, not exploitation.
Each result shows its source dates. A negative interval means the end event came first; when date-only inputs leave the order open, the result says so. Date-only inputs are approximate. The earliest evidence wins: KEV report dates and sightings are labelled as such. Records describing another vulnerability are listed but never calculated from, and a PoC alone does not establish exploitation. Missing patch evidence does not prove that no patch exists. Filters below change the event list only.
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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
model, served locally by ML-Gateway.
They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
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Related by attack behaviour
Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.