sapp has a global CPU-load-based 'under_ddos' bypass mode: once realtime CPU usage on a worker thread exceeds a configurable threshold (95% in the shipped default), sapp enters a global bypass state in which matched streams skip all plugin processing (no classification, no blocking) until load recovers, smoothed via an EWMA and a multi-second recovery-observation window. A separate anti_flood.conf additionally hard-drops SYN floods above 15000pps and UDP/DNS floods above 1000pps at the packet-filter level, while explicitly whitelisting DNS (port 53) and SIP (port 5060) from that drop.
to reduce impact of ddos attack,set some stream bypass, all plugins will not process these streams / sapp change to bypass state immediately when realtime cpu usage > bypass_trigger_cpu_usage / bypass_trigger_cpu_usage=95
Defense implications
- A CPU-exhaustion condition on the inspection box causes sapp to fail-open (skip DPI/blocking entirely) rather than fail-closed, which is a real (if operationally risky and adversarially detectable) avenue to empirically test — sustained load near the trigger threshold could create windows where circumvention traffic passes uninspected.
Cited artifacts
mesalab_git—MESA_Platform/sapp.bundle(git-commit-log)
Provenance pointers only — no leak content is rehosted. Raw material: Enlace Hacktivista.
Related findings
An internal TSG operations/troubleshooting manual lays out TSG's full traffic pipeline (NIC -> mrzcpd/marsio capture driver -> sapp DPI engine -> firewall/proxy(KNI->TFE)/active-defense/WAN-NAT policy branches) and shows engineers using maat_redis_tool to pull the live Redis-synced blocking policy tables (TSG_SECURITY_COMPILE, TSG_OBJ_IP_ADDR, TSG_OBJ_APP_ID) and filter them by numeric policy/object ID to debug why a block rule isn't firing.
The internal 'MAAT网络流处理配置统一描述框架' engineering manual (v3.1.20, author 郑超, 2021) documents MAAT's Redis-synced rule-compilation framework and its RuleScan/Hyperscan-based pattern-matching engine (libmaatframe.so / librulescan), and records that RuleScan's fast-scan feature caused a production outage on 2019-03-19 and has been disabled ever since.
An internal MESA Lab report (2021-06-25) documents a live test in which a second sapp instance ('sapp B') receives fully decrypted plaintext HTTP traffic via a Unix domain socket from a third-party TLS decryption platform, while sapp A separately captures raw ciphertext via the mrzcpd driver. 24 hours of the decrypted logs (319,569 HTTP records) show the top intercepted destinations are Facebook, Twitter, Google/YouTube and Instagram, with client IPs traced to residential China Telecom/Unicom/Mobile subscribers in Guangdong, Zhejiang and other provinces.
Raw structured DNS event logs (dated 2021-08-23) captured from what appears to be a GFW-adjacent DNS monitoring/injection pipeline use a schema purpose-built for DNS response forgery ('CHEAT_TYPE', 'CHEAT_RCODE', 'CHEAT_STRATEGY', 'CHEAT_RR', 'INJECTED_PKT_FILE' fields) alongside per-query geolocation; sampled records show lookups for facebook.com and tiktokv.com originating from residential China Telecom/Unicom/Mobile subscriber IPs in Guangdong, Zhejiang, Anhui and other provinces, resolving against both domestic and foreign (8.8.8.8, OpenDNS) resolvers.
A 2023 MESA Lab monthly report describes the 'TF' project's active-defense work: test cases for serial ('串联') HTTP hijack/tamper and parallel ('并联') DNS race-injection ('DNS抢答'), performance tuning that scaled active-defense capacity from 3 to 5 units, converting two existing TSG boxes to active-defense mode, and rewriting the active-defense flow-control logic to no longer depend on sapp.
The same 224-column TSG per-session log schema carries a full TLS- interception field set — proxy_pinning_status, proxy_intercept_status, proxy_passthrough_reason, proxy_cert_verify, proxy_intercept_error, sc_rsp_raw and sc_rsp_decrypted (raw vs. decrypted server response content) — plus ssl_esni_flag and ssl_ech_flag (explicit ECH/ESNI-usage flags), ssl_ja3_hash/ssl_ja3s_hash, and ssh_hassh (SSH client fingerprinting), confirming certstore-style MITM interception, ECH/ESNI detection, and TLS/SSH fingerprinting are all first-class fields logged on every session, not experimental add-ons.