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CVE-2026-103471 – Unauthenticated Denial of Service – Restbed ≤5.0.0

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Summary

CVE-2026-103471 is a high-severity denial-of-service vulnerability in Restbed, the C++ REST API framework maintained by Corvusoft. The framework buffers incoming HTTP request headers without enforcing any maximum size limit, allowing a remote, unauthenticated attacker to send an endless stream of bytes without the terminating header delimiter and force the server to allocate memory until it exhausts available heap and crashes. The issue is tracked as CWE-770 (Allocation of Resources Without Limits or Throttling) and carries a CVSS score of 8.7.

Technical details

  • Root cause: In src/corvusoft/restbed/detail/service_impl.cpp, Restbed uses Asio’s async_read_until() to read incoming HTTP request data into a buffer, waiting for the rnrn header-terminator sequence before parsing. No upper bound is placed on how large this buffer may grow while waiting for the delimiter.
  • Trigger condition: An attacker opens a TCP connection to a Restbed-based server and continuously streams arbitrary bytes without ever sending the rnrn sequence that marks the end of HTTP headers.
  • Attack vector: Network-based, requires no authentication and no user interaction — any client capable of reaching the exposed service (typically an HTTP port) can trigger it.
  • Impact: The server keeps appending data to the unbounded buffer, causing heap memory consumption to increase without limit. This can lead to memory exhaustion and process termination, resulting in denial of service for all users of the affected service. A single connection is sufficient to cause impact, and the attack can be repeated or run over multiple connections to amplify effect.

Affected software

  • Restbed (Corvusoft) versions 0 through 5.0.0 (all released versions up to and including 5.0.0)

Severity

  • CVSS v3.1 Base Score: 7.5 (HIGH) — Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
  • CVSS v4.0 Base Score: 8.7 (HIGH) — Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
  • No confidentiality or integrity impact; impact is limited to availability.

Mitigation and recommended actions

  • Immediate: As of the CVE publication, no official patched release of Restbed addressing this issue has been confirmed. Security teams should monitor the Corvusoft/restbed GitHub repository and the tracking issue for a fixed release, and upgrade as soon as a patched version is available.
  • Workarounds / network mitigations (no patch yet available):
    • Place a reverse proxy or load balancer (e.g., one that enforces request header size limits and connection/read timeouts) in front of any Restbed-based service to reject oversized or slow, never-terminating requests before they reach the application.
    • Configure strict idle/read timeouts and maximum request size limits at the network or proxy layer to close connections that fail to complete HTTP headers within a reasonable time.
    • Apply connection-rate limiting and per-source connection caps to reduce the ability of a single attacker to exhaust server resources.
    • If feasible, restrict direct network exposure of Restbed-based services and require access through a hardened intermediary.

References

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