{"id":"CVE-2026-110353","kind":"vulnerability","aliases":["CVE-2026-110353"],"related":[],"title":"HAProxy: truncated HTTP/2 PING frame spins worker threads, causing denial of service","description":"HAProxy 3.2 before 3.4.6 allows a remote unauthenticated attacker to cause a denial of service (worker-thread CPU exhaustion) via a truncated HTTP/2 PING frame. h2c_handle_ping in src/mux_h2.c does not check for a short read, unlike the other H2 frame handlers. Because the incomplete frame cannot be processed, its data is never consumed, and the H2 multiplexer tasklet is repeatedly woken by that pending data without making progress. The CPU spins until timeout http-request closes the connection, and an attacker opening many such connections can sustain high CPU usage.","summary":"HAProxy 3.2 before 3.4.6 does not check for short reads in its HTTP/2 PING frame handler, so a truncated PING leaves data unconsumed and the multiplexer tasklet spins. An unauthenticated remote attacker opening many such connections can exhaust worker-thread CPU and deny service.","severity":"high","cvss":7.5,"epss":0.00684,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["haproxy","http2","load-balancer","runtime","self-hosted"],"not_affected_if":["default-config"],"how_to_check":"- Run `haproxy -v` and check whether the version is 3.2.x below `3.4.6`.\n- Check whether HTTP/2 is enabled on a frontend (`proto h2` or `alpn h2` in the `bind` line of `haproxy.cfg`).","fix":"- Upgrade HAProxy to `3.4.6` or later.\n- Until upgraded, the sources do not name a configuration workaround: unknown.","status":"open","published_at":"2026-10-22T03:16:31+00:00","first_seen_at":"2026-10-23T21:57:30+00:00","triaged_at":"2026-10-25T03:16:14+00:00","updated_at":"2026-10-25T03:16:14+00:00","category":"runtime","confidence":0.7,"triage":{"at":"2026-10-25T03:16:14Z","model":"claude-haiku-5-5","output":{"fix":"- Upgrade HAProxy to `3.4.6` or later.\n- Until upgraded, the sources do not name a configuration workaround: unknown.","reach":"internet","title":"HAProxy: truncated HTTP/2 PING frame spins worker threads, causing denial of service","impact":"medium","summary":"HAProxy 3.2 before 3.4.6 does not check for short reads in its HTTP/2 PING frame handler, so a truncated PING leaves data unconsumed and the multiplexer tasklet spins. An unauthenticated remote attacker opening many such connections can exhaust worker-thread CPU and deny service.","category":"runtime","nicknames":[],"who_cares":["haproxy","load-balancer","self-hosted","http2"],"confidence":0.7,"needs_auth":"no","worst_case":"Attacker exhausts worker-thread CPU, degrading or halting proxy service.","analyst_note":"","how_to_check":"- Run `haproxy -v` and check whether the version is 3.2.x below `3.4.6`.\n- Check whether HTTP/2 is enabled on a frontend (`proto h2` or `alpn h2` in the `bind` line of `haproxy.cfg`).","needs_analyst":false,"not_affected_if":["default-config"],"who_is_affected":"HAProxy 3.2 releases before 3.4.6 that accept HTTP/2 connections from the internet or an untrusted network are exposed, since the attack needs no credentials. Deployments that do not serve HTTP/2 on a bind line, or that run a different HAProxy line, are not described as affected by the sources.","user_interaction":"no","needs_special_setup":"unknown","severity_if_unknown":"high"},"cost_usd":0.000645,"input_tokens":3479,"output_tokens":595,"severity_before":"high"},"analyst_status":null,"analyst_note":null,"search":"'-110353':15A,18A '-2026':14A,17A '3.2':29B,74C '3.4.6':31B,76C 'allow':77C 'attack':59B,81C,157C 'balanc':23B 'cannot':121C 'caus':9A,83C 'check':34B,106C 'close':152C 'connect':63B,154C,161C 'consum':128C 'cpu':69B,91C,145C,165C 'cve':13A,16A 'data':49B,125C,140C 'deni':71B 'denial':10A,85C 'exhaust':65B,92C 'frame':5A,42B,98C,115C,120C 'h2':114C,131C 'h2c':99C 'handl':100C 'handler':43B,116C 'haproxi':1A,19B,28B,73C 'high':164C 'host':27B 'http':150C 'http-request':149C 'http/2':3A,40B,96C 'http2':20B 'incomplet':119C 'leav':48B 'load':22B 'load-balanc':21B 'make':142C 'mani':61B,159C 'multiplex':53B,132C 'never':127C 'open':60B,158C 'pend':139C 'ping':4A,41B,47B,97C,101C 'process':123C 'progress':143C 'read':37B,110C 'remot':58B,79C 'repeat':135C 'request':151C 'runtim':24B 'self':26B 'self-host':25B 'servic':12A,72B,87C 'short':36B,109C 'spin':6A,55B,146C 'src/mux_h2.c':103C 'sustain':163C 'tasklet':54B,133C 'thread':8A,68B,90C 'timeout':148C 'truncat':2A,46B,95C 'unauthent':57B,80C 'unconsum':50B 'unlik':111C 'usag':166C 'via':93C 'without':141C 'woken':136C 'worker':7A,67B,89C 'worker-thread':66B,88C","nicknames":[],"mitigations":[],"who_affected":"HAProxy 3.2 releases before 3.4.6 that accept HTTP/2 connections from the internet or an untrusted network are exposed, since the attack needs no credentials. Deployments that do not serve HTTP/2 on a bind line, or that run a different HAProxy line, are not described as affected by the sources.","tier":"B","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-10-22T03:16:31+00:00","kev":null,"cvss_vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","cvss_by":"cve@mitre.org","poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-110353","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-110353","severity":null,"published_at":"2026-10-22T03:16:31+00:00","modified_at":"2026-10-22T19:17:35+00:00","first_seen_at":"2026-10-23T21:57:30+00:00","fetched_at":"2026-10-23T22:29:02+00:00","note":null},{"source":"epss","external_id":"CVE-2026-110353","url":"https://api.first.org/data/v1/epss?cve=CVE-2026-110353","severity":null,"published_at":null,"modified_at":null,"first_seen_at":"2026-10-24T07:15:52+00:00","fetched_at":"2026-10-24T07:15:52+00:00","note":null}],"documents":[],"notice":"Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai"}