Security incident · CVE-2026-114437

chi: Client IP spoofing in ClientIPFromXFF via X-Forwarded-For

Q: Which versions are affected?

Compare what you have installed with 0 → 5.4.0, <= 5.3.2. Compare the installed version with the linked vendor advisory before you change production.

Q: What should an analyst verify?

CWE-345: Insufficient Verification of Data Authenticity. EPSS 0.13%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Published Oct 23, 2026 · catalog updated Oct 23, 2026 · chi: Client IP spoofing

Last checked Nov 6, 2026. A connected source was read within the last 7 days.

Check if you run it

No confirmed exploitation is on record for CVE-2026-114437. EPSS is 0.13%. Act only if a listed version of chi: Client IP spoofing is installed.

Gaps on this record

The stored product name is a package slug. The name on this page is taken from the title (chi: Client IP spoofing).
No vendor fix or required action is stored. Compare the linked advisory before you change production.

Severity: Medium4.8
Known exploitation: Not in CISA/VulnCheck KEV
EPSS: 0.13%
Remediation: Version ranges on file
Affected products: Go github.com/go-chi/chi/v5 · go github.com/go-chi/chi/v5 · golang github.com

### Summary skips any entry in a configured trusted CIDR but never verifies that the direct TCP peer in belongs to that CIDR. A client that can reach the Go server directly can therefore append a trusted-looking proxy address and choose the client IP returned by . The attack is remote and requires one unauthenticated HTTP request with no user interaction (AV:N/AC:L/PR:N/UI:N). It changes security decisions and exposes one protected handler within the same application (S:U/C:L/I:L); no availability loss was observed (A:N). **Preconditions:** The application uses and makes the origin server reachable by an anonymous client outside the configured trusted-proxy CIDRs. No victim interaction is required. 1. Send directly to the origin with no header. 2. Observe a response and an empty derived client IP. 3. Repeat the request with . 4. Observe and . Expected: the untrusted direct peer prevents the forwarding chain from being accepted. ### Details The vulnerable code is in , lines 93-116 at the tested revision. It calls with only the attacker-controlled header, skips every entry that matches a trusted prefix, and stores the first remaining address: The function does not parse before this walk. Consequently, the configured CIDRs identify trusted strings inside , but do not establish that the immediate sender is one of those trusted proxies. ### Proof of concept Using Go 1.24 or later, create and run this minimal application against the tested revision: The no-header control was rejected: Adding the forged chain authorized the same direct client: ### Impact I made an anonymous direct connection from , supplied a header that ended in a different trusted-proxy CIDR, and caused the application to treat my client IP as the allowlisted . This changed the authorization decision from to for the protected handler.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

Go github.com/go-chi/chi/v50 → 5.4.0
go github.com/go-chi/chi/v5<= 5.3.2
golang github.comversion unspecified

How to fix CVE-2026-114437

Upgrade
CVE-2026-114437 lists a fix boundary at 5.4.0. Compare the installed build with that boundary before you change production.
Version check
Affected <= 5.3.2
Advisory
Open the cve_org record and follow its fix.
Official advisories

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-114437. EPSS is 0.13%. Act only if a listed version of chi: Client IP spoofing is installed.

Which versions are affected?

Compare what you have installed with 0 → 5.4.0, <= 5.3.2. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-345: Insufficient Verification of Data Authenticity. EPSS 0.13%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

Repository · github.com

Timeline

Detection, updates, and resolution for this record.

Oct 23, 2026 · GitHub Advisory Database
Detected
### Summary skips any entry in a configured trusted CIDR but never verifies that the direct TCP peer in belongs to that CIDR. A client that can reach the Go server directly can therefore append a trusted-looking proxy address and choose the client IP returned by . The attack is remote and requires one unauthenticated HTTP request with no user interaction (AV:N/AC:L/PR:N/UI:N). It changes security
Oct 23, 2026 · GitHub Advisory Database
Fix available
github.com/go-chi/chi/v5 fixed in 5.4.0
Oct 23, 2026 · GitHub Advisory Database
Fix available
github.com/go-chi/chi/v5 fixed in 5.4.0
Oct 23, 2026 · GitHub Advisory Database
Updated
### Summary skips any entry in a configured trusted CIDR but never verifies that the direct TCP peer in belongs to that CIDR. A client that can reach the Go server directly can therefore append a trusted-looking proxy address and choose the client IP returned by . The attack is remote and requires one unauthenticated HTTP request with no user interaction (AV:N/AC:L/PR:N/UI:N). It changes security

Sources

CVE.orgVulnerability recordCVE-2026-114437
Official CVE identifier
cve.org
FIRST EPSSExploitation probabilityCVE-2026-114437
30-day exploitation probability 0.13%
first.org
GitHub Advisory DatabasePackage advisoryGHSA-j6qf-3m9c-vwj3
GitHub Advisory Database record mirrored by OSV.
github.com
GitLab Advisory DatabasePackage advisoryCVE-2026-114437
ClientIPFromXFF skips any X-Forwarded-For entry in a configured trusted CIDR but never verifies that the direct TCP peer in http.Request.RemoteAddr belongs to that CIDR. A client that can reach the Go server directly can therefore append a trusted-looking proxy address and choose the client IP returned by middleware.GetClientIP. The attack is remote and requires one unauthenticated HTTP request wi
advisories.gitlab.com
Go Vulnerability DatabasePackage advisoryGHSA-j6qf-3m9c-vwj3
chi: Client IP spoofing in ClientIPFromXFF via X-Forwarded-For
osv.dev
OpenSSF OSV / OSV ScannerPackage advisoryGHSA-j6qf-3m9c-vwj3
chi: Client IP spoofing in ClientIPFromXFF via X-Forwarded-For
osv.dev

References

Freshness

Last verified in this catalog Nov 6, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.

FIRST EPSSNov 6, 2026
Go Vulnerability DatabaseOct 28, 2026
GitLab Advisory DatabaseOct 27, 2026
GitHub Advisory DatabaseOct 26, 2026
OpenSSF OSV / OSV ScannerOct 26, 2026
CVE.orgOct 24, 2026

Priority score

8/100

Evidence confidence: High

Several independent sources name this vulnerability.

Confirmed exploitation0/30
EPSS probability1/20
CVSS severity7/15
Public exploit0/10
Internet exposure0/10
Product prevalence0/5
Detection0/5
Threat research0/5

Decision signals

Four separate signals — do not infer one from another.

Medium

CVSS severity
4.8 v3.1
Technical impact. Separate from exploitation likelihood.
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N
EPSS probability
0.13% · p2.56%
Estimated probability of exploitation within 30 days (FIRST).
Known exploitation
No verified KEV listing
Evidence from CISA KEV or VulnCheck KEV only — not from EPSS alone.
Patch availability
Version ranges on file
Affected version ranges suggest a fixed boundary. Verify against the vendor advisory for your release.

Stacks

Weakness

CWE-345
Insufficient Verification of Data Authenticity
MITRE definition

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