[engine] caught signal (SIGSEGV)

[krisiasty]

Bug Report

Describe the bug
fluent-bit is crashing every couple of minutes with error:

Dec 15 11:18:35 svc01 fluent-bit[76937]: [2025/12/15 11:18:35] [engine] caught signal (SIGSEGV)
Dec 15 11:18:35 svc01 fluent-bit[76937]: #0  0x60d27033b964      in  ares_slist_node_claim() at lib/c-ares-1.34.4/src/lib/dsa/ares_slist.c:295
Dec 15 11:18:35 svc01 fluent-bit[76937]: #1  0x60d27032d29c      in  ares_destroy_servers_state() at lib/c-ares-1.34.4/src/lib/ares_destroy.c:153
Dec 15 11:18:35 svc01 fluent-bit[76937]: #2  0x60d27032d3cd      in  ares_destroy() at lib/c-ares-1.34.4/src/lib/ares_destroy.c:96
Dec 15 11:18:35 svc01 fluent-bit[76937]: #3  0x60d26ff04999      in  flb_net_dns_lookup_context_destroy() at src/flb_network.c:670
Dec 15 11:18:35 svc01 fluent-bit[76937]: #4  0x60d26ff04999      in  flb_net_dns_lookup_context_cleanup() at src/flb_network.c:709
Dec 15 11:18:35 svc01 fluent-bit[76937]: #5  0x60d26ff0b8a1      in  flb_engine_start() at src/flb_engine.c:1280
Dec 15 11:18:35 svc01 fluent-bit[76937]: #6  0x60d26fede727      in  flb_lib_worker() at src/flb_lib.c:904
Dec 15 11:18:35 svc01 fluent-bit[76937]: #7  0x72cc6fe9caa3      in  ???() at ???:0
Dec 15 11:18:35 svc01 fluent-bit[76937]: #8  0x72cc6ff29c6b      in  ???() at ???:0
Dec 15 11:18:35 svc01 fluent-bit[76937]: #9  0xffffffffffffffff  in  ???() at ???:0
Dec 15 11:18:35 svc01 systemd[1]: fluent-bit.service: Main process exited, code=dumped, status=6/ABRT
Dec 15 11:18:35 svc01 systemd[1]: fluent-bit.service: Failed with result 'core-dump'.
Dec 15 11:18:36 svc01 systemd[1]: fluent-bit.service: Scheduled restart job, restart counter is at 6.

To Reproduce
The configuration is very simple - there are few prometheus scrapers collecting metrics from several node exporters running on the localhost (127.0.0.1) on various ports. The scrape interval is set to 10s.
The metrics are then exported via remote write to external host running Cortex.
Both parsers.conf and plugins.conf came unmodified from official distribution.

[SERVICE]
    flush        10
    daemon       Off
    log_level    info
    parsers_file parsers.conf
    plugins_file plugins.conf

# scrape prometheus metrics and send to cortex
[INPUT]
    name           prometheus_scrape
    tag            metrics.local.recursor
    host           127.0.0.1
    port           8053
    metrics_path   /metrics
    scrape_interval 10s

[INPUT]
    name           prometheus_scrape
    tag            metrics.local.dnsdist
    host           127.0.0.1
    port           8853
    metrics_path   /metrics
    scrape_interval 10s

[INPUT]
    name          fluentbit_metrics
    tag           metrics.local.internal
    scrape_interval  10s

[OUTPUT]
    name                 prometheus_remote_write
    match                metrics.local.*
    host                 monitoring.example.com
    port                 443
    uri                  /api/v1/push
    header               X-Scope-OrgID tenant-id
    http_user            username
    http_passwd          password
    tls                  on
    tls.verify           on
    log_response_payload true
    add_label            instance ${HOSTNAME}

Your Environment

• Version used: v4.2.0
• Configuration:
• Environment name and version (e.g. Kubernetes? What version?): linux kvm virtual machine
• Server type and version:
• Operating System and version: latest Ubuntu minimal cloud image ubuntu-minimal-24.04-20251113
• Filters and plugins: