CVE-2026-73253: Mongoose is an embedded web server and network library

Q: How do I fix CVE-2026-73253?

mongoose: upgrade to 7.22. Exact commands for each OS are on this page.

Q: Is CVE-2026-73253 being exploited?

CVE-2026-73253 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-2026-73253 affect?

CVE-2026-73253 affects mongoose. Severity is critical (CVSS 9.1). Mongoose is an embedded web server and network library. Prior to version 7.22, an on-path network attacker with a wildcard certificate for a parent domain can impersonate deeper subdomains to a client using the built-in TLS stack. The mg_tl

Q: How urgent is CVE-2026-73253?

Priority 49/100. Critical severity; Public exploit reference; Remotely exploitable, no login, no user action

This week

CRITICAL 9.1REMOTEUPGRADE

CVE-2026-73253 is a critical-severity flaw (CVSS 9.1) affecting mongoose. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Mongoose is an embedded web server and network library. Prior to version 7.22, an on-path network attacker with a wildcard certificate for a parent domain can impersonate deeper subdomains to a client using the built-in TLS stack. The mg_tls_verify_cert_san() and mg_tls_verify_cert_cn() functions in src/tls_builtin.c call mg_match(), whose wildcard can cross DNS label boundaries, so a pattern such as *.example.com can match foo.bar.example.com. T

Why this priority

Critical severity
Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	9.1 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.3% (top 72%)
CISA exploited list	No
Weakness	CWE-295
Published	2026-08-20
Last modified	2026-10-18

Publisher (CNA): GitHub, Inc. · Vendor: cesanta

Last updated 2026-10-18 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-08-20 18:16 UTCPublished CVE record published
2026-10-18 20:10 UTCUpdated Record last modified

cesanta mongoose UPGRADE

Affected: < 7.22

Fixed in: 7.22

Safe to downgrade to: no unaffected older release

1. Check installed version

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

2. UPGRADE to 7.22 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade mongoose

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-2026-73253?

mongoose: upgrade to 7.22. Exact commands for each OS are on this page.

Is CVE-2026-73253 being exploited?

CVE-2026-73253 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-2026-73253 affect?

CVE-2026-73253 affects mongoose. Severity is critical (CVSS 9.1). Mongoose is an embedded web server and network library. Prior to version 7.22, an on-path network attacker with a wildcard certificate for a parent domain can impersonate deeper subdomains to a client using the built-in TLS stack. The mg_tl

How urgent is CVE-2026-73253?

Priority 49/100. Critical severity; Public exploit reference; Remotely exploitable, no login, no user action

Related CVEs

CVE-2026-5244 HIGH 7.3 UPGRADE A vulnerability has been found in Cesanta Mongoose up to 7.20
CVE-2026-6985 MEDIUM 5.3 UPGRADE A weakness has been identified in Cesanta Mongoose up to 7.20
CVE-2026-5246 MEDIUM 5.6 UPGRADE A vulnerability was determined in Cesanta Mongoose up to 7.20
CVE-2026-5245 MEDIUM 5.6 UPGRADE A vulnerability was found in Cesanta Mongoose up to 7.20
CVE-2026-6986 LOW 3.7 UPGRADE A security vulnerability has been detected in Cesanta Mongoose up to 7.20

References

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