{"id":"CVE-2026-109088","kind":"vulnerability","aliases":["CVE-2026-109088"],"related":[],"title":"libXtst: malformed X server reply causes client endless loop","description":"A malicious X server could send malformed  RECORD EnableContext reolies that can cause a X client using the parse_reply_call_callback function in libXtst before 1.2.6 to enter a endless loop.","summary":"A malicious X server can send malformed RECORD EnableContext replies to an X client using libXtst before 1.2.6. The client then enters an endless loop, which stalls or hangs the program.","severity":"medium","cvss":6.5,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["infrastructure","libxtst","linux","self-hosted","x11"],"not_affected_if":["libxtst-1.2.6-or-later","trusted-x-server-only"],"how_to_check":"- Find the installed libXtst version, for example with `pkg-config --modversion xtst` or `dpkg -l libxtst6`, and check whether it is below `1.2.6`.\n- Check whether programs linking libXtst connect to X servers you do not control.","fix":"- Upgrade libXtst to `1.2.6` or later through your OS package manager.","status":"open","published_at":"2026-10-27T17:16:57+00:00","first_seen_at":"2026-10-27T17:32:45+00:00","triaged_at":"2026-10-27T17:34:49+00:00","updated_at":"2026-10-27T17:34:49+00:00","category":"infrastructure","confidence":0.6,"triage":{"at":"2026-10-27T17:34:49Z","model":"claude-haiku-5-5","output":{"fix":"- Upgrade libXtst to `1.2.6` or later through your OS package manager.","reach":"network","title":"libXtst: malformed X server reply causes client endless loop","impact":"low","summary":"A malicious X server can send malformed RECORD EnableContext replies to an X client using libXtst before 1.2.6. The client then enters an endless loop, which stalls or hangs the program.","category":"infrastructure","nicknames":[],"who_cares":["x11","libxtst","linux","self-hosted"],"confidence":0.6,"needs_auth":"no","worst_case":"Client program hangs in an endless loop, denying service.","analyst_note":"","how_to_check":"- Find the installed libXtst version, for example with `pkg-config --modversion xtst` or `dpkg -l libxtst6`, and check whether it is below `1.2.6`.\n- Check whether programs linking libXtst connect to X servers you do not control.","needs_analyst":false,"not_affected_if":["trusted-x-server-only","libxtst-1.2.6-or-later"],"who_is_affected":"Systems with X11 clients that use libXtst's RECORD extension against an X server that may be untrusted, such as remote X forwarding or connecting to a display on another host. A local desktop talking only to its own trusted X server is less exposed. The sources do not describe a default configuration that exposes it.","user_interaction":"unknown","needs_special_setup":"unknown","severity_if_unknown":"medium"},"cost_usd":0.000582,"input_tokens":3279,"output_tokens":508,"severity_before":"medium"},"analyst_status":null,"analyst_note":null,"search":"'-109088':12A,15A '-2026':11A,14A '1.2.6':40B,80C 'call':74C 'callback':75C 'caus':6A,66C 'client':7A,36B,42B,69C 'could':58C 'cve':10A,13A 'enablecontext':31B,62C 'endless':8A,46B,84C 'enter':44B,82C 'function':76C 'hang':51B 'host':21B 'infrastructur':16B 'libxtst':1A,17B,38B,78C 'linux':18B 'loop':9A,47B,85C 'malform':2A,29B,60C 'malici':24B,55C 'pars':72C 'program':53B 'record':30B,61C 'reoli':63C 'repli':5A,32B,73C 'self':20B 'self-host':19B 'send':28B,59C 'server':4A,26B,57C 'stall':49B 'use':37B,70C 'x':3A,25B,35B,56C,68C 'x11':22B","nicknames":[],"mitigations":[],"who_affected":"Systems with X11 clients that use libXtst's RECORD extension against an X server that may be untrusted, such as remote X forwarding or connecting to a display on another host. A local desktop talking only to its own trusted X server is less exposed. The sources do not describe a default configuration that exposes it.","tier":"C","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-10-27T17:16:57+00:00","kev":null,"cvss_vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H","cvss_by":"meissner@suse.de","poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-109088","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-109088","severity":null,"published_at":"2026-10-27T17:16:57+00:00","modified_at":"2026-10-27T17:16:57+00:00","first_seen_at":"2026-10-27T17:32:45+00:00","fetched_at":"2026-10-27T17:32:45+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"}