VulnerabilityPublished 29 Oct 2026

CVE-2026-115877: HTTP Request Smuggling in twisted.web via a Bare CR or LF in a Header Value

Affects magic-wormholeSource GCVE Database

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Authoritative record:CVE-2026-115877· Medium 5.4

Not known to be exploited · CVSS 5.4 Medium.

Data as of 30 Oct 2026, 07:30 UTC

CVSS 3.1 base score

5.4Medium

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

Thin evidence

One scorer or none

CVSS scores by source
CNA (GitHub_M)	CVSS 3.1	5.4

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

Attack Vector: Network
Attack Complexity: High
Privileges Required: None
User Interaction: None
Scope: Changed
Confidentiality: Low
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: High: A successful attack depends on conditions beyond the attacker's control. That is, a successful attack cannot be accomplished at will, but requires the attacker to invest in some measurable amount of effort in preparation or execution against the vulnerable component before a successful attack can be expected. For example, a successful attack may require an attacker to: gather knowledge about the environment in which the vulnerable target/component exists; prepare the target environment to improve exploit reliability; or inject themselves into the logical network path between the target and the resource requested by the victim in order to read and/or modify network communications (e.g., a man in the middle attack).
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: Changed: An exploited vulnerability can affect resources beyond the security scope managed by the security authority of the vulnerable component. In this case, the vulnerable component and the impacted component are different and managed by different security authorities.
Confidentiality: Low: There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to 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 23 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: 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 29 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.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), 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

Affected software

Product	Affected	Fixed in
Homebrewmagic-wormhole`pkg:brew/magic-wormhole`Other threats	Affected >=0.9.2	Fixed in–

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

Description

## Summary An incomplete header-value validation (CWE-444) in the Twisted HTTP server lets a bare carriage return or line feed in a header value hide a following header from the parser. `twisted.web.http.HTTPChannel.headerReceived` rejects a NUL byte in a header value but not a bare CR or LF, even though RFC 9110 section 5.5 requires a recipient to reject all three. Because the channel splits requests only on CRLF, a value carrying a bare LF and a second header arrives as one line, so the second header is folded into the value and the request is framed with no body. A front-end that treats the bare LF as a line terminator frames the request differently, and the disagreement lets an attacker smuggle a request past it. This is an incomplete fix of the earlier Twisted request-smuggling advisories, which guarded the NUL sibling of this exact check. ## Details `headerReceived` splits a header line on the first colon, strips space and tab from the value, and validates it with a single test that rejects only NUL: ```python # twisted/web/http.py HTTPChannel.headerReceived data = data.strip(b" \t") if b"\x00" in data: # NUL rejected; a bare CR or LF is not self._respondToBadRequestAndDisconnect() return False ``` The channel delimiter is CRLF, so `Foo: x\nContent-Length: 39` is one line: the split yields name `Foo` and value `x\nContent-Length: 39`, `strip` leaves the LF, and the NUL check passes. `_maybeChooseTransferDecoder` is then called with `Foo`, never sees a `Content-Length`, and installs no body decoder, so the request is framed with an empty body. The header name and request line already reject CR and LF, so the value is the only gap. Affected product: Twisted, `twisted.web.http.HTTPChannel` Affected versions: 26.4.0 and earlier ## PoC Feed one connection a request whose header value carries a bare LF and a `Content-Length`, followed by a second request in the bytes after it: `POST /public HTTP/1.1\r\nHost: v\r\nFoo: x\nContent-Length: 44\r\n\r\nGET /admin HTTP/1.1\r\nHost: internal\r\n\r\n`. Twisted parses two requests and serves both, so the smuggled `GET /admin` returns the /admin response body even though the visible request was only `POST /public`. The bare CR variant behaves identically, and a NUL in the value is rejected, which isolates the missing CR and LF checks. Behind a front-end that treats the bare LF as a line terminator, the front-end frames one `POST /public` and forwards a body while Twisted frames a second `GET /admin`; the extra response then poisons the shared connection, so a later victim receives the attacker's `GET /admin` response. ## Impact This is an HTTP request-smuggling exposure (CWE-444) from inconsistent interpretation of a request (CWE-436). Through a front-end that accepts a bare CR or LF as a line terminator, an attacker can smuggle a request the front-end never sees, bypassing front-end access controls, poisoning a shared connection so a later victim receives the attacker's response, and poisoning a cache. Twisted is the strict endpoint that frames the request without a body, so it is realized only behind such a proxy, and there is no code execution.

References

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