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CVE-2026-57577 – Denial of Service (ReDoS) – DotVVM Routing (versions before 4.2.11, 4.3.0–4.3.14, 5

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Summary

CVE-2026-57577 is a Regular Expression Denial of Service (ReDoS) vulnerability in DotVVM, an open-source MVVM framework for building web applications on .NET. Applications that define routes with multiple unconstrained parameters in a single path segment are vulnerable to catastrophic regex backtracking in the route-matching engine, allowing a remote, unauthenticated attacker to exhaust server CPU resources. The issue has a CVSS score of 8.2 (High).

Technical details

  • Root cause: DotvvmRouteParser.RouteRegex, used internally by DotvvmRoute.IsMatch, previously had no matching timeout, so pathological input could drive the .NET regex engine into excessive backtracking.
  • Trigger conditions: the application must define a route containing multiple unconstrained parameters within a single path segment without a literal separator (e.g. a pattern like edit/{a}-{b}-{c}/done).
  • Attack vector: network — an attacker sends a specially crafted, long, "near-match" URL path (e.g. thousands of dash characters) to the vulnerable route.
  • Impact: excessive CPU consumption during route matching, leading to service degradation or denial of service; no confidentiality or integrity impact.

Affected software

  • DotVVM versions prior to 4.2.11
  • DotVVM 4.3.0 up to (but not including) 4.3.15
  • DotVVM 5.0.0-preview01 up to (but not including) 5.0.0-preview09-final

Severity

CVSS score: 8.2 (High)
Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Mitigation and recommended actions

  • Immediate: upgrade to DotVVM 4.2.11, 4.3.15, or 5.0.0-preview09-final (or later), which apply a one-second timeout to route-matching regex operations and fall back to the .NET non-backtracking regex engine (on .NET 8.0+) or return HTTP 503 when the timeout is exceeded.
  • If immediate patching is not possible:
    • Add explicit constraints to route parameters (e.g. {param:alpha}) to eliminate character-type ambiguity.
    • Use regex constraints such as {param:regex([^-]*)} to exclude problematic separator characters from matching.
    • Separate multiple route parameters with literal path separators (/) rather than placing them adjacently in a single segment.

References

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