CVE-2021-27565: The web server in InterNiche NicheStack through 4.0.1 allows remote attackers to cause a denial of service (in

Q: How do I fix CVE-2021-27565?

nichestack: upgrade to newer than 4.0.1. Exact commands for each OS are on this page.

Q: Is CVE-2021-27565 being exploited?

CVE-2021-27565 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2021-27565 affect?

CVE-2021-27565 affects nichestack. Severity is high (CVSS 7.5). The web server in InterNiche NicheStack through 4.0.1 allows remote attackers to cause a denial of service (infinite loop and networking outage) via an unexpected valid HTTP request such as OPTIONS. This occurs because the HTTP request hand

Q: How urgent is CVE-2021-27565?

Priority 53/100. High severity; Remotely exploitable, no login, no user action

This month

HIGH 7.5REMOTEUPGRADE

CVE-2021-27565 is a high-severity flaw (CVSS 7.5) affecting nichestack. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

The web server in InterNiche NicheStack through 4.0.1 allows remote attackers to cause a denial of service (infinite loop and networking outage) via an unexpected valid HTTP request such as OPTIONS. This occurs because the HTTP request handler enters a miscoded wbs_loop() debugger hook.

Why this priority

High severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	2.6% (top 15%)
CISA exploited list	No
Weakness	CWE-835
Published	2021-08-19
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: hcc-embedded

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2021-08-19 12:15 UTCPublished CVE record published
2026-06-17 03:45 UTCUpdated Record last modified

hcc-embedded nichestack UPGRADE

Affected: <= 4.0.1

Fixed in: newer than 4.0.1

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy nichestack || rpm -q nichestack || nichestack --version

2. UPGRADE to newer than 4.0.1 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade nichestack

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade nichestack

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2021-27565?

nichestack: upgrade to newer than 4.0.1. Exact commands for each OS are on this page.

Is CVE-2021-27565 being exploited?

CVE-2021-27565 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2021-27565 affect?

CVE-2021-27565 affects nichestack. Severity is high (CVSS 7.5). The web server in InterNiche NicheStack through 4.0.1 allows remote attackers to cause a denial of service (infinite loop and networking outage) via an unexpected valid HTTP request such as OPTIONS. This occurs because the HTTP request hand

How urgent is CVE-2021-27565?

Priority 53/100. High severity; Remotely exploitable, no login, no user action

Related CVEs

CVE-2021-36762 HIGH 7.5 UPGRADE An issue was discovered in HCC Embedded InterNiche NicheStack through 4.3
CVE-2021-31401 HIGH 7.5 UPGRADE UPGRADE An issue was discovered in tcp_rcv() in nptcp.c in HCC embedded InterNiche 4.0.1
CVE-2021-31400 HIGH 7.5 UPGRADE An issue was discovered in tcp_pulloutofband() in tcp_in.c in HCC embedded InterNiche 4.0.1
CVE-2021-31228 HIGH 7.5 UPGRADE An issue was discovered in HCC embedded InterNiche 4.0.1
CVE-2021-31227 HIGH 7.5 UPGRADE An issue was discovered in HCC embedded InterNiche 4.0.1

References

← Back to latest CVEs