EUVD-2026-83255
GHSA-f27v-pv5m-c5g6
Severity by source
CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Network-reachable and unauthenticated (AV:N/PR:N), but AC:H because success depends on cache state and an origin emitting wildcard Vary; pure confidentiality disclosure so C:H, I:N, A:N.
Primary rating from Vendor (VulnCheck).
CVSS VectorVendor: VulnCheck
Lifecycle Timeline
3DescriptionCVE.org
http-cache-semantics through 4.2.0 contains a cache validation vulnerability in the _varyMatches() function that fails to properly validate Vary header wildcards due to byte-for-byte string comparison. Attackers can request URLs previously fetched by other clients to receive cached responses intended for different users, disclosing sensitive information across clients.
AnalysisAI
Cross-client information disclosure in http-cache-semantics through 4.2.0 allows remote, unauthenticated attackers to receive cached responses that were generated for other users. The library's _varyMatches() function performs byte-for-byte comparison of Vary header values and therefore fails to treat a wildcard 'Vary: *' directive as a prohibition on shared-cache reuse, so a request for a URL previously fetched by someone else can be satisfied from cache with that other client's sensitive per-user data. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Requires http-cache-semantics to be used as a SHARED cache serving multiple distinct clients/users (not a private per-user cache), AND an origin server that returns a wildcard Vary header (Vary: *) on a cacheable response containing sensitive per-user data. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The vendor CVSS 4.0 base score is 8.2 (AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N), driven almost entirely by high confidentiality impact on a network-reachable, unauthenticated path - but tempered by AC:H and AT:P, which correctly reflect that exploitation is conditional and non-deterministic rather than a straightforward request. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | Full exploit scenario with step-by-step reproduction available after sign-in. |
| Remediation | No vendor-released patch was identified at time of analysis; the upstream tracking issue (https://github.com/kornelski/http-cache-semantics/issues/57) is the authoritative place to confirm when a fixed release appears, and until then the library should be treated as unfixed on the 4.2.0-and-earlier line. … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours, inventory every Node.js service and caching layer that transitively includes http-cache-semantics at version 4.2.0 or earlier (common consumers include cacheable-request and the got ecosystem), and identify origins that emit a wildcard 'Vary: *' header on cacheable responses. …
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External POC / Exploit Code
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