CVE-2021-42338: 4MOSAn GCB Doctor’s login page has improper validation of Cookie, which allows an unauthenticated remote attac

Q: How do I fix CVE-2021-42338?

gcb doctor: upgrade to newer than 20210708. Exact commands for each OS are on this page.

Q: Is CVE-2021-42338 being exploited?

CVE-2021-42338 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-2021-42338 affect?

CVE-2021-42338 affects gcb doctor. Severity is critical (CVSS 9.8). 4MOSAn GCB Doctor’s login page has improper validation of Cookie, which allows an unauthenticated remote attacker to bypass authentication by code injection in cookie, and arbitrarily manipulate the system or interrupt services by upload an

Q: How urgent is CVE-2021-42338?

Priority 63/100. Critical severity; EPSS top 7%: very likely to be exploited; Remotely exploitable, no login, no user action

This week

CRITICAL 9.8REMOTEUPGRADE

CVE-2021-42338 is a critical-severity flaw (CVSS 9.8) affecting gcb doctor. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

4MOSAn GCB Doctor’s login page has improper validation of Cookie, which allows an unauthenticated remote attacker to bypass authentication by code injection in cookie, and arbitrarily manipulate the system or interrupt services by upload and execution of arbitrary files.

Why this priority

Critical severity
EPSS top 7%: very likely to be exploited
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	5.8% (top 7%)
CISA exploited list	No
Weakness	CWE-285, CWE-287
Published	2021-11-19
Last modified	2026-06-17

Publisher (CNA): TWCERT/CC · Vendor: 4mosan

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

Am I affected?

Timeline

2021-11-19 09:15 UTCPublished CVE record published
2026-06-17 04:09 UTCUpdated Record last modified

4mosan gcb doctor UPGRADE

Affected: <= 20210708

Fixed in: newer than 20210708

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy gcb-doctor || rpm -q gcb-doctor || gcb-doctor --version

2. UPGRADE to newer than 20210708 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade gcb-doctor

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade gcb-doctor

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-2021-42338?

gcb doctor: upgrade to newer than 20210708. Exact commands for each OS are on this page.

Is CVE-2021-42338 being exploited?

CVE-2021-42338 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-2021-42338 affect?

CVE-2021-42338 affects gcb doctor. Severity is critical (CVSS 9.8). 4MOSAn GCB Doctor’s login page has improper validation of Cookie, which allows an unauthenticated remote attacker to bypass authentication by code injection in cookie, and arbitrarily manipulate the system or interrupt services by upload an

How urgent is CVE-2021-42338?

Priority 63/100. Critical severity; EPSS top 7%: very likely to be exploited; Remotely exploitable, no login, no user action

Related CVEs

CVE-2021-44159 CRITICAL 9.8 UPGRADE 4MOSAn GCB Doctor’s file upload function has improper user privilege control

References

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