Improper Validation of Syntactic Correctness of Input vulnerability in mtrudel bandit allows an unauthenticated remote attacker to set conn.host and conn.port to values outside the RFC 3986 host grammar via the authority of an HTTP/1 absolute-form or authority-form request target. Bandit validates the Host header and answers 400 when it is malformed, but when the request target carries its own authority that authority takes precedence, as RFC 9112 requires, and Bandit.Pipeline.determine_host_and_port!/4 in lib/bandit/pipeline.ex passes it to the application unchecked. A request line such as GET http://good.example@evil.example/x HTTP/1.1 with a valid Host header yields a conn.host of good.example@evil.example, and the same path admits NUL, DEL and non-ASCII bytes, invalid IP literals and ports outside 1..65535. The HTTP/1.0 clause needs no Host header at all, and CONNECT places the unparsed port string in conn.port.
Applications that build absolute URLs from conn.host, such as through Plug.Conn.request_url/1 or Phoenix URL helpers, emit links whose authority the attacker chose. Message framing is unaffected, and no CR or LF can reach conn.host.
This issue affects bandit: from 0.6.0 before 1.13.0.
What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)
The EG score (6.9): severity, escalated by confirmed exploitation. This CVE's 6.9 is its impact severity (EG Severity), not escalated.
- EG Severity
- 6.9 MEDIUMCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.a secondary CVSS source · CVSS v3.0 or v3.1
- EG Likelihood
- 0.6% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-10-28). FIRST's exploitation probability, not an EchelonGraph model.
- Confirmed exploitation
- None on record (CISA KEV, EG-KEV Tier 1)Reported apart from the likelihood: an observed fact, not a probability.
- EG Priority
- SSVC Track at medium mission impactTrack at low or medium mission impact; Attend at high (mission-essential systems).CISA BOD 26-04: 14 days if the affected system is publicly exposed; 60 days if it is not.Each input and its source, and whom BOD 26-04 binds: the SSVC and BOD 26-04 blocks below.
SSVC (CISA's decision table, applied by EchelonGraph)Track at low or medium mission impact; Attend at high (mission-essential systems).
A fix is available. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.
Exploitation public PoC (CISA Vulnrichment) · Automatable yes (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table
BOD 26-04 (CISA's remediation timeline, Table 1)14 days if the affected system is publicly exposed; 60 days if it is not.
The score's inputs: In CISA KEV no (CISA's KEV catalog) · Automatable yes (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it