HTTP 500 "Error: socket hang up" on CAS
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HTTP 500 "Error: socket hang up" on CAS

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Article ID: 454027

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ISG Content Analysis

Issue/Introduction

The customer is using REST API to send files to the CAS.

The upload intermittently fails with the below error:

HTTP/1.1 500 (body, 154 bytes total): Error: socket hang up

Cause

From the CAS SOS report we could see the following log entries that matched the customer error message:

2026-08-06T17:14:54.073115+03:00 CAS avenger[3285708]: WARNING : WebRouter::IncomingConnect: socket hang up
2026-08-06T17:14:54.558158+03:00 CAS avenger-webrouter-443[20672]: TLS incoming connect error: socket hang up
2026-08-06T17:14:54.573181+03:00 CAS avenger[3285718]: WARNING : WebRouter::IncomingConnect: socket hang up
2026-08-06T17:14:54.737728+03:00 CAS avenger-webrouter-443[20672]: TLS incoming connect error: socket hang up
2026-08-06T17:14:54.747958+03:00 CAS avenger[3285723]: WARNING : WebRouter::IncomingConnect: socket hang up
2026-08-06T17:15:12.507383+03:00 CAS avenger-webrouter-443[20672]: TLS incoming connect error: socket hang up
2026-08-06T17:15:12.520000+03:00 CAS avenger[3286412]: WARNING : WebRouter::IncomingConnect: socket hang up
2026-08-06T17:15:13.610389+03:00 CAS avenger-webrouter-443[20672]: TLS incoming connect error: socket hang up
2026-08-06T17:15:13.626049+03:00 CAS avenger[3286434]: WARNING : WebRouter::IncomingConnect: socket hang up
2026-08-06T17:15:14.264280+03:00 CAS avenger-webrouter-443[20672]: TLS incoming connect error: socket hang up
2026-08-06T17:15:14.276187+03:00 CAS avenger[3286558]: WARNING : WebRouter::IncomingConnect: socket hang up
2026-08-06T17:15:23.925674+03:00 CAS avenger-webrouter-443[20672]: TLS incoming connect error: socket hang up
2026-08-06T17:15:23.942862+03:00 CAS avenger[3287047]: WARNING : WebRouter::IncomingConnect: socket hang up
2026-08-06T17:15:25.013261+03:00 CAS avenger-webrouter-443[20672]: TLS incoming connect error: socket hang up
2026-08-06T17:15:25.025014+03:00 CAS avenger[3287054]: WARNING : WebRouter::IncomingConnect: socket hang up
 

Looking at a provided pcap that overlapped with the connect error messages we could see the following 3 tcp stream:

The behaviour see int he PCAP above can be summarise as:

  1. the client sends a TCP SYN request to the CAS
  2. CAS responds with the expected TCP SYN-ACK
  3. the client sends a TLS Client Hello message to the CAS
  4. CAS sends a TCP ACK (for the client hello message packet)
  5. CAS send the TLS Server Hello to the client
  6. the client sends a TLS Change Cipher message to the CAS
  7. the client sends a TCP RESET to the CAS

Resolution

As we can see in the PCAP the TLS exchange is interrupted by the client before the connection was fully setup.

The problem is not related to the CAS configuration or operations but rather with the client (a proxy).

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