VulnerabilityPublished 4 Oct 2026Updated 27 Oct 2026

CVE-2026-84379: HTTPX2 · Multipart part header injection via unvalidated file Content-Type and custom headers

Affects hermes-agentSource GCVE Database

Authoritative record:CVE-2026-84379· Medium 5.3

Not known to be exploited · CVSS 5.3 Medium : upgrade to 0.22.2 when convenient.

Data as of 27 Oct 2026, 21:00 UTC

CVSS 3.1 base score

5.3Medium

How severe the flaw is on the 0–10 CVSS scale.

Patch: Available – fixed in 0.22.2

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: Low
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact on the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 2 Sep 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade hermes-agent to 0.22.2.

Affected software

Product	Affected	Fixed in
Homebrewhermes-agent`pkg:brew/hermes-agent`Other threats	Affected >=0.21.6 <0.22.2 >=2026.8.31_1 <=2026.9.24	Fixed in 0.22.2

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Upgrade to HTTPX2 version 0.22.2 or later, which includes validation rejecting forbidden control characters in multipart part header names and values and raises ValueError before serialization. If immediate upgrade is not possible, validate and sanitize per-file Content-Type and custom header names and values to reject NUL, CR, LF, other C0 controls except horizontal tab, and DEL characters before passing them to HTTPX2.

Description

HTTPX2 versions before 0.22.2 improperly serialize per-file Content-Type and custom headers in multipart/form-data requests without validating for control characters. This allows an attacker controlling upload metadata to inject CR or LF characters, enabling multipart part header injection. The impact depends on how the receiving server processes multipart headers, potentially altering part semantics or bypassing header-based checks. The issue is fixed in HTTPX2 version 0.22.2.

Impact

An attacker able to control per-file Content-Type or custom headers can inject multipart part headers into the request body. This can modify the interpretation of multipart parts by the receiving server, potentially bypassing validation or altering upload semantics. The vulnerability does not affect the outer HTTP request headers and does not lead to request splitting. The overall impact depends on the server's multipart parsing and application logic. The CVSS score is 5.3 (medium severity) with no confidentiality or availability impact but limited integrity impact.

Summary

HTTPX2's multipart serialization accepts per-file Content-Type and custom headers via its files= tuple API and directly inserts them into the multipart/form-data body without validating header names or values for forbidden control characters. Attackers who can influence these inputs may inject CR or LF characters to prematurely terminate or add multipart part headers, altering the multipart body structure. This vulnerability affects HTTPX2 versions >=0.21.6 and <0.22.2. The vulnerability does not affect field names or filenames, which are escaped separately. The security impact depends on the downstream multipart parser's handling of injected headers. The issue is resolved in HTTPX2 0.22.2, which rejects forbidden control characters and raises errors before serialization.

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 27 Oct 2026, 21:00 UTC

Technical details

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