CVE-2026-73256: Mongoose is an embedded web server and network library

Q: How do I fix CVE-2026-73256?

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

Q: Is CVE-2026-73256 being exploited?

CVE-2026-73256 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-2026-73256 affect?

CVE-2026-73256 affects mongoose. Severity is critical (CVSS 9.1). Mongoose is an embedded web server and network library. Prior to 7.22, a remote unauthenticated attacker can exploit an HTTP/1.0 reverse-proxy deployment by sending a request with Transfer-Encoding: chunked and conflicting framing. The http

Q: How urgent is CVE-2026-73256?

Priority 51/100. Critical severity; Public exploit reference; Remotely exploitable, no login, no user action

This week

CRITICAL 9.1REMOTEUPGRADE

CVE-2026-73256 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 7.22, a remote unauthenticated attacker can exploit an HTTP/1.0 reverse-proxy deployment by sending a request with Transfer-Encoding: chunked and conflicting framing. The http_cb() function in src/http.c tests hm.proto.len with an impossible greater-than-eight condition even though mg_http_parse() requires an eight-byte protocol string, so is_http_1_0 is never set. Mongoose conseque

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	0.4% (top 62%)
CISA exploited list	No
Weakness	CWE-444
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-2026-73256?

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

Is CVE-2026-73256 being exploited?

CVE-2026-73256 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-2026-73256 affect?

CVE-2026-73256 affects mongoose. Severity is critical (CVSS 9.1). Mongoose is an embedded web server and network library. Prior to 7.22, a remote unauthenticated attacker can exploit an HTTP/1.0 reverse-proxy deployment by sending a request with Transfer-Encoding: chunked and conflicting framing. The http

How urgent is CVE-2026-73256?

Priority 51/100. 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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