{"id":"CVE-2026-117556","kind":"vulnerability","aliases":["CVE-2026-117556"],"related":[],"title":"zchunk: crafted .zck file triggers heap out-of-bounds read and crash","description":"zchunk before 1.5.5 contains a heap out-of-bounds read vulnerability in read_preface() in src/lib/header.c that passes the total header length instead of remaining bytes to compint parsing functions. Attackers can supply a crafted .zck file whose header ends inside a compressed integer, causing reads past the heap header buffer and crashing the application.","summary":"zchunk before 1.5.5 passes the total header length instead of the remaining bytes to its compressed-integer parser in read_preface(). A crafted .zck file whose header ends mid-integer makes the parser read past the heap buffer, crashing the application.","severity":"medium","cvss":5.3,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["dnf","linux-packaging","package","zchunk"],"not_affected_if":["zchunk-1.5.5-or-later"],"how_to_check":"- Run `zck --version` or check the installed zchunk package version; versions below `1.5.5` are affected.\n- unknown","fix":"- Upgrade zchunk to `1.5.5` or later.","status":"open","published_at":"2026-10-27T14:16:36+00:00","first_seen_at":"2026-10-27T14:32:19+00:00","triaged_at":"2026-10-27T14:33:10+00:00","updated_at":"2026-10-27T14:33:10+00:00","category":"package","confidence":0.6,"triage":{"at":"2026-10-27T14:33:10Z","model":"claude-haiku-5-5","output":{"fix":"- Upgrade zchunk to `1.5.5` or later.","reach":"unknown","title":"zchunk: crafted .zck file triggers heap out-of-bounds read and crash","impact":"low","summary":"zchunk before 1.5.5 passes the total header length instead of the remaining bytes to its compressed-integer parser in read_preface(). A crafted .zck file whose header ends mid-integer makes the parser read past the heap buffer, crashing the application.","category":"package","nicknames":[],"who_cares":["zchunk","linux-packaging","dnf"],"confidence":0.6,"needs_auth":"no","worst_case":"Application crashes on a crafted .zck file.","analyst_note":"","how_to_check":"- Run `zck --version` or check the installed zchunk package version; versions below `1.5.5` are affected.\n- unknown","needs_analyst":false,"not_affected_if":["zchunk-1.5.5-or-later"],"who_is_affected":"Systems that parse .zck files from untrusted sources with zchunk before 1.5.5, such as package tooling that downloads zchunk-compressed repository metadata. The sources describe a crash, not code execution, and do not say which downstream tools embed the library.","user_interaction":"unknown","needs_special_setup":"no","severity_if_unknown":"medium"},"cost_usd":0.000565,"input_tokens":3345,"output_tokens":460,"severity_before":"medium"},"analyst_status":null,"analyst_note":null,"search":"'-117556':16A,19A '-2026':15A,18A '1.5.5':28B,71C 'applic':68B,124C 'attack':100C 'bound':10A,78C 'buffer':65B,120C 'byte':38B,95C 'caus':114C 'compint':97C 'compress':42B,112C 'compressed-integ':41B 'contain':72C 'craft':2A,49B,104C 'crash':13A,66B,122C 'cve':14A,17A 'dnf':20B 'end':54B,109C 'file':4A,51B,106C 'function':99C 'header':32B,53B,90C,108C,119C 'heap':6A,64B,74C,118C 'insid':110C 'instead':34B,92C 'integ':43B,57B,113C 'length':33B,91C 'linux':22B 'linux-packag':21B 'make':58B 'mid':56B 'mid-integ':55B 'out-of-bound':7A,75C 'packag':23B,24B 'pars':98C 'parser':44B,60B 'pass':29B,87C 'past':62B,116C 'prefac':47B,83C 'read':11A,46B,61B,79C,82C,115C 'remain':37B,94C 'src/lib/header.c':85C 'suppli':102C 'total':31B,89C 'trigger':5A 'vulner':80C 'whose':52B,107C 'zchunk':1A,25B,26B,69C 'zck':3A,50B,105C","nicknames":[],"mitigations":[],"who_affected":"Systems that parse .zck files from untrusted sources with zchunk before 1.5.5, such as package tooling that downloads zchunk-compressed repository metadata. The sources describe a crash, not code execution, and do not say which downstream tools embed the library.","tier":"C","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-10-27T14:16:36+00:00","kev":null,"cvss_vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","cvss_by":"disclosure@vulncheck.com","poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-117556","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-117556","severity":null,"published_at":"2026-10-27T14:16:36+00:00","modified_at":"2026-10-27T14:16:36+00:00","first_seen_at":"2026-10-27T14:32:19+00:00","fetched_at":"2026-10-27T14:32:19+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"}