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Directory Transversal Vulnerability in Serv-U 15.3

Not in CISA KEVCVE-2021-35250CWE-22

Not confirmed exploited. 1 of 8 rule sources name it. Our CRS test: blocked.

Edge rules
1/8
Our test
Blocked
CVSS
7.5
EPSS
12.8% Top 4%
Posts, 14d
02026-10-21: 0 posts2026-10-22: 0 posts2026-10-23: 0 posts2026-10-24: 0 posts2026-10-25: 0 posts2026-10-26: 0 posts2026-10-27: 0 posts2026-10-28: 0 posts2026-10-29: 0 posts2026-10-30: 0 posts2026-10-31: 0 posts2026-11-01: 0 posts2026-11-02: 0 posts2026-11-03: 0 posts
Published
2022-04-25

A researcher reported a Directory Transversal Vulnerability in Serv-U 15.3. This may allow access to files relating to the Serv-U installation and server files. This issue has been resolved in Serv-U 15.3 Hotfix 1.

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Ask about CVE-2021-35250: who's covered, what to patch first, how vendors compare. I cite sources and won't help with attacks.

Workers AI (Llama 3.3). Can be wrong: check the cited source.

Severity, decoded

CVSS 3.1
High · 7.5 / 10

Exploitable over the network, with no privileges and no user interaction, leading to full loss of confidentiality.

Over the internetNo login neededNo user actionWorks reliablySerious impact
How the score is built8 metrics
  • Attack vectorAn attacker can reach it over the internet; no access to your network needed.
    Network
  • Attack complexityNo special conditions are needed; the attack works reliably.
    Low
  • Privileges requiredNo account or login is needed.
    None
  • User interactionNo one has to click or open anything; the attack works on its own.
    None
  • ScopeThe damage stays within the vulnerable component.
    Unchanged
  • Confidentiality impactAn attacker can read all data the affected component holds, or the most sensitive parts of it.
    High
  • Integrity impactData cannot be changed by the attacker.
    None
  • Availability impactThe component keeps working normally.
    None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Public exploits

1 found
0 Metasploit0 Exploit-DB1 Scanner template0 GitHub PoCs

Links are to third-party code: never run it outside an isolated lab.

Timeline

  1. 2022-04-25
    CVE published
    CVE List
  2. 2024-05-21
    F5 ships a rule
    SolarWinds Serv-U Directory Traversal
  3. 2026-11-02
    Our test: OWASP Core Rule Set blocked it
    paranoia level 1, anomaly threshold 5, default CRS settings
  4. 2026-11-02
    Our test: OWASP Core Rule Set blocked it
    paranoia level 2, anomaly threshold 5, default CRS settings

Social

2026-10-21: 0 posts2026-10-22: 0 posts2026-10-23: 0 posts2026-10-24: 0 posts2026-10-25: 0 posts2026-10-26: 0 posts2026-10-27: 0 posts2026-10-28: 0 posts2026-10-29: 0 posts2026-10-30: 0 posts2026-10-31: 0 posts2026-11-01: 0 posts2026-11-02: 0 posts2026-11-03: 0 posts

No posts seen yet on X, Bluesky, Mastodon, Hacker News or GitHub.

Vendor statements

Quoted
CloudflareWAF Managed RulesBefore feed history

The CVE predates the oldest entry in this vendor's public feed, so a rule may exist that we cannot see.

AWSAWS WAF Managed RulesNo public claim

We found no public statement from this vendor naming this CVE. That is not proof of no protection: generic rules may still catch it. AWS often describes a vulnerability without naming its CVE (for example "Log4j"). We count only entries that name the CVE, so AWS coverage is understated.

Microsoft AzureFront Door and Application Gateway WAF (DRS)No public claim

We found no public statement from this vendor naming this CVE. That is not proof of no protection: generic rules may still catch it. The rule tables name CVEs but carry no dates, so Azure is left out of every time-to-rule figure.

Google CloudCloud Armor preconfigured WAF rulesBefore feed history

The CVE predates the oldest entry in this vendor's public feed, so a rule may exist that we cannot see.

FastlyNext-Gen WAF virtual patchesBefore feed history

The CVE predates the oldest entry in this vendor's public feed, so a rule may exist that we cannot see.

F5Attack signatures (Distributed Cloud WAF)1 quoteRule published

First rule 2024-05-21, 757 days after the CVE was published.

2024-05-21New rule200007063Source
Added: signature 200007063 "SolarWinds Serv-U Directory Traversal" (Path Traversal, risk High), systems: Other Web Server. References: CVE-2021-35250.
AkamaiApp & API Protector (Adaptive Security Engine)No public source

This vendor publishes no machine-readable rule changelog we can check.

OWASP CRSCore Rule Set (open source, used inside many WAFs)Before feed history

The CVE predates the oldest entry in this vendor's public feed, so a rule may exist that we cannot see.