CVE-2026-33131 [High] | Spoofing in H3

H3 is a minimal H(TTP) framework. Versions 2.0.0-0 through 2.0.1-rc.14 contain a Host header spoofing vulnerability in the NodeRequestUrl (which extends FastURL) which allows middleware bypass. When event.url, event.url.hostname, or event.url._url is accessed, such as in a logging middleware, the _url getter constructs a URL from untrusted data, including the user-controlled Host header. Because H3's router resolves the route handler before middleware runs, an attacker can supply a crafted Host header (e.g., Host: localhost:3000/abchehe?) to make the middleware path check fail while the route handler still matches, effectively bypassing authentication or authorization middleware. This affects any application built on H3 (including Nitro/Nuxt) that accesses event.url properties in middleware guarding sensitive routes. The issue requires an immediate fix to prevent FastURL.href from being constructed with unsanitized, attacker-controlled input. Version 2.0.1-rc.15 contains a patch for this issue.

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#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2026-03-20	—	0.04%	—

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Old EPSS score

New EPSS score

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2026-03-20

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0.04%

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Base score	Version	Severity	Vector	Exploitability	Impact	Score source
7.4	3.1	HIGH	`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N` Click to expand Attack vector (AV:N) Could be attacked over the internet or any normal routed network—not just someone sitting at the machine. Attack complexity (AC:H) Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work. Privileges required (PR:N) No account or special rights needed—anonymous or random user is enough. User interaction (UI:N) Nobody has to click “OK” or open a trap file; it can work without a victim helping. Scope (S:U) Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems. Confidentiality (C:H) Serious risk that confidential data gets exposed in a big way. Integrity (I:H) They could widely tamper with or forge data—trust in the data is badly hurt. Availability (A:N) Service keeps running; no real outage angle.	2.2	5.2	[email protected]
9.1	3.1	CRITICAL	`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N` Click to expand Attack vector (AV:N) Could be attacked over the internet or any normal routed network—not just someone sitting at the machine. Attack complexity (AC:L) Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup. Privileges required (PR:N) No account or special rights needed—anonymous or random user is enough. User interaction (UI:N) Nobody has to click “OK” or open a trap file; it can work without a victim helping. Scope (S:U) Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems. Confidentiality (C:H) Serious risk that confidential data gets exposed in a big way. Integrity (I:H) They could widely tamper with or forge data—trust in the data is badly hurt. Availability (A:N) Service keeps running; no real outage angle.	3.9	5.2	[email protected]

Base score

Version

Severity

Vector

Exploitability

Impact

Score source

7.4

3.1

HIGH

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N Click to expand

Attack vector (AV:N): Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:H): Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:N): No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N): Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U): Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H): Serious risk that confidential data gets exposed in a big way.
Integrity (I:H): They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:N): Service keeps running; no real outage angle.

2.2

5.2

[email protected]

9.1

3.1

CRITICAL

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N Click to expand

Attack vector (AV:N): Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L): Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N): No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N): Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U): Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H): Serious risk that confidential data gets exposed in a big way.
Integrity (I:H): They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:N): Service keeps running; no real outage angle.

3.9

5.2

[email protected]

Affected software / configurations for CVE-2026-33131

Vendor	Product	Version	Raw CPE
h3	h3	2.0.0	cpe:2.3:a:h3:h3:2.0.0:::::node.js::
h3	h3	2.0.1	cpe:2.3:a:h3:h3:2.0.1:rc10::::node.js::*
h3	h3	2.0.1	cpe:2.3:a:h3:h3:2.0.1:rc11::::node.js::*
h3	h3	2.0.1	cpe:2.3:a:h3:h3:2.0.1:rc12::::node.js::*
h3	h3	2.0.1	cpe:2.3:a:h3:h3:2.0.1:rc13::::node.js::*
h3	h3	2.0.1	cpe:2.3:a:h3:h3:2.0.1:rc14::::node.js::*
h3	h3	2.0.1	cpe:2.3:a:h3:h3:2.0.1:rc2::::node.js::*
h3	h3	2.0.1	cpe:2.3:a:h3:h3:2.0.1:rc3::::node.js::*
h3	h3	2.0.1	cpe:2.3:a:h3:h3:2.0.1:rc4::::node.js::*
h3	h3	2.0.1	cpe:2.3:a:h3:h3:2.0.1:rc5::::node.js::*
h3	h3	2.0.1	cpe:2.3:a:h3:h3:2.0.1:rc6::::node.js::*
h3	h3	2.0.1	cpe:2.3:a:h3:h3:2.0.1:rc7::::node.js::*
h3	h3	2.0.1	cpe:2.3:a:h3:h3:2.0.1:rc8::::node.js::*
h3	h3	2.0.1	cpe:2.3:a:h3:h3:2.0.1:rc9::::node.js::*

References for CVE-2026-33131

URL	Tags
https://github.com/h3js/h3/security/advisories/GHSA-3vj8-jmxq-cgj5	Exploit Vendor Advisory

URL

CVE-2026-33131 | h3 has a middleware bypass with one gadget

Public exploit references (Exploit-DB) for CVE-2026-33131

Exploit prediction scoring system (EPSS) score for CVE-2026-33131

Common vulnerability scoring system (CVSS) metrics for CVE-2026-33131

Weakness enumeration for CVE-2026-33131

GitHub Security Advisory for CVE-2026-33131

Affected software / configurations for CVE-2026-33131

References for CVE-2026-33131