CWE-178: Improper Handling of Case Sensitivity

The product does not properly account for differences in case sensitivity when accessing or determining the properties of a resource, leading to inconsistent results.

Improperly handled case sensitive data can lead to several possible consequences, including: case-insensitive passwords reducing the size of the key space, making brute force attacks easier bypassing filters or access controls using alternate names multiple interpretation errors using alternate names.

Consequences

• Access Control: Bypass Protection Mechanism

How to prevent it

• Architecture and Design: Avoid making decisions based on names of resources (e.g. files) if those resources can have alternate names.
• Implementation: Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
• Implementation: Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174). Such errors could be used to bypass allowlist validation schemes by introducing dangerous inputs after they have been checked.

Recent advisories

• GHSA-vjh5-4x84-xrqp — Nuxt: Server-side route rules (`redirect`, `headers`, `proxy`, `ssr`) are skipped for case-variant paths when routing is case-insensitive
• GHSA-f72v-6w45-q472 — undici vulnerable to Subresource Integrity bypass via non-lowercase algorithm tokens
• GHSA-389g-gv7q-r4x8 — fastify is vulnerable to header validation bypass via case-sensitive propertyNames
• GHSA-hmp2-4m7g-22cv — Backstage: Scaffolder action input authorization bypass
• GHSA-hrr3-gc8f-f4qj — fast-uri vulnerable to inconsistent host case normalization via percent-encoded octets
• GHSA-9q9j-q6p8-xq58 — fastify vulnerable to header validation bypass via incomplete schema case normalization
• GHSA-qc2q-p7wx-3px3 — gRPC-Go: xDS RBAC HTTP Filter bypass via mixed-case Header Matching and gRFC A41 validation evasion
• GHSA-6mj3-qw4j-hgrw — xmldom: HTML raw-text closing-tag case mismatch causes output amplification
• EEF-CVE-2026-82726 — AshPhoenix get_subdomain maps a crafted or differently-cased Host header to an arbitrary tenant
• GHSA-hxvh-4h3w-prp9 — Nuxt route rules silently dropped for mixed-case paths, bypassing appMiddleware auth gates (incomplete fix for CVE-2026-53721)
• GHSA-vwg3-w8w3-pc79 — Grav: .htaccess file extension rules bypass via case variation on case-insensitive filesystems
• GHSA-x677-9fxg-v5c5 — Traefik: Incomplete fix for CVE-2026-33433 + CVE-2026-39858 cross-cohort: headerField underscore-variant identity spoofing in BasicAuth / DigestAuth / ForwardAuth
• GHSA-8678-w3jw-xfc2 — Nokogiri: XML::Schema on JRuby allows network requests when NONET is set, bypassing CVE-2020-26247
• GHSA-cf98-j28v-49v6 — OpenFGA Improper Policy Enforcement
• GHSA-mm7m-92g8-7m47 — Nuxt: Route-rule middleware bypass via case-sensitivity mismatch between vue-router and the routeRules matcher

All advisories for CWE-178