{"id":"CVE-2026-123792","kind":"vulnerability","aliases":["CVE-2026-123792"],"related":[],"title":"Symfony Yaml: crafted YAML document stalls PHP worker, causing denial of service","description":"The Symfony Yaml components Inline and Parser, parse some YAML documents inefficiently, so that a small crafted document can take disproportionately long to process, keeping a PHP process busy for seconds or minutes, potentially causing a denial of service in Symfony versions prior to 5.4.56, 6.x prior to 6.4.50, 7.x prior to 7.4.23, and 8.x prior to 8.1.11.\n\nThe parser repeats work it has already done in several places. An embedded mapping in a flow sequence is parsed again for every scalar appended to it, and so are the collections nested in it, so the parse time grows exponentially with the nesting depth. The patterns matching mapping keys and tags scan a run of spaces once per character of the run, and each scalar of a flow collection is matched against a copy of the rest of the collection, so the parse time grows quadratically with the size of the input. Nested blocks are also copied at each nesting level, which consumes memory as well as time. A few other constructs, such as an empty sequence item followed by a blank line or an anchor named 0, trigger similar repeated work.\n\n\nAny code parsing untrusted YAML is affected, with the default flags. In Symfony 7.4 and later, that includes #[MapRequestPayload] when the Yaml component is installed and the endpoint does not restrict acceptFormat. A single unauthenticated request with a YAML content type keeps a PHP worker busy until max_execution_time. JSON documents are valid YAML, so a JSON payload sent with a YAML content type is enough for the flow collection case. In Symfony 6.4, #[MapRequestPayload] accepts YAML only when the application registers a yaml request format.","summary":"Symfony's Yaml component parses some documents inefficiently, so parse time grows exponentially or quadratically with input size. A small crafted YAML document can keep a PHP process busy for seconds or minutes, causing denial of service.","severity":"high","cvss":8.7,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["maprequestpayload","package","php","symfony","symfony/yaml"],"not_affected_if":["acceptformat-restricted","no-untrusted-yaml","no-yaml-request-format"],"how_to_check":"- Check the installed `symfony/yaml` version with `composer show symfony/yaml` and compare it with the fixed versions below.\n- Search for `#[MapRequestPayload]` on endpoints in Symfony 7.4 or later, and check whether `acceptFormat` is restricted.\n- In Symfony 6.4, check whether the application registers a `yaml` request format.","fix":"- symfony/yaml: upgrade to `5.4.56` on the 5.4 line, `6.4.50` on 6.4, `7.4.23` on 7.4, or `8.1.11` on 8.x.","status":"open","published_at":"2026-11-06T16:17:55+00:00","first_seen_at":"2026-11-06T16:42:41+00:00","triaged_at":"2026-11-06T16:44:42+00:00","updated_at":"2026-11-06T16:44:42+00:00","category":"package","confidence":0.8,"triage":{"at":"2026-11-06T16:44:42Z","model":"claude-haiku-5-5","output":{"fix":"- symfony/yaml: upgrade to `5.4.56` on the 5.4 line, `6.4.50` on 6.4, `7.4.23` on 7.4, or `8.1.11` on 8.x.","reach":"internet","title":"Symfony Yaml: crafted YAML document stalls PHP worker, causing denial of service","impact":"medium","summary":"Symfony's Yaml component parses some documents inefficiently, so parse time grows exponentially or quadratically with input size. A small crafted YAML document can keep a PHP process busy for seconds or minutes, causing denial of service.","audience":"developers","category":"package","nicknames":[],"who_cares":["symfony","php","symfony/yaml","maprequestpayload"],"confidence":0.8,"fix_status":"available","needs_auth":"no","worst_case":"PHP worker pinned until timeout; denial of service.","analyst_note":"","how_to_check":"- Check the installed `symfony/yaml` version with `composer show symfony/yaml` and compare it with the fixed versions below.\n- Search for `#[MapRequestPayload]` on endpoints in Symfony 7.4 or later, and check whether `acceptFormat` is restricted.\n- In Symfony 6.4, check whether the application registers a `yaml` request format.","plain_action":"","needs_analyst":false,"not_affected_if":["no-untrusted-yaml","acceptformat-restricted","no-yaml-request-format"],"who_is_affected":"Any PHP application that parses untrusted YAML is affected with default flags. In Symfony 7.4 and later, endpoints using #[MapRequestPayload] are exposed when the Yaml component is installed and acceptFormat is not restricted. In Symfony 6.4, exposure requires the application to register a yaml request format.","user_interaction":"no","needs_special_setup":"no","severity_if_unknown":"high"},"cost_usd":0.001413,"input_tokens":4733,"output_tokens":1880,"severity_before":"high"},"analyst_status":null,"analyst_note":null,"search":"'-123792':15A,18A '-2026':14A,17A '0':250C '5.4.56':105C '6':106C '6.4':329C '6.4.50':110C '7':111C '7.4':268C '7.4.23':115C '8':117C '8.1.11':121C 'accept':331C 'acceptformat':286C 'affect':261C 'alreadi':128C 'also':218C 'anchor':248C 'append':146C 'applic':336C 'blank':244C 'block':216C 'busi':52B,89C,300C 'case':326C 'caus':9A,57B,95C 'charact':181C 'code':256C 'collect':153C,191C,202C,325C 'compon':27B,64C,277C 'construct':234C 'consum':225C 'content':294C,318C 'copi':196C,219C 'craft':3A,44B,77C 'cve':13A,16A 'default':264C 'denial':10A,58B,97C 'depth':166C 'disproportion':81C 'document':5A,30B,46B,71C,78C,306C 'done':129C 'embed':134C 'empti':238C 'endpoint':282C 'enough':321C 'everi':144C 'execut':303C 'exponenti':36B,162C 'flag':265C 'flow':138C,190C,324C 'follow':241C 'format':341C 'grow':35B,161C,207C 'includ':272C 'ineffici':31B,72C 'inlin':65C 'input':40B,214C 'instal':279C 'item':240C 'json':305C,312C 'keep':48B,85C,296C 'key':171C 'later':270C 'level':223C 'line':245C 'long':82C 'map':135C,170C 'maprequestpayload':19B,273C,330C 'match':169C,193C 'max':302C 'memori':226C 'minut':56B,93C 'name':249C 'nest':154C,165C,215C,222C 'packag':20B 'pars':28B,33B,68C,141C,159C,205C,257C 'parser':67C,123C 'pattern':168C 'payload':313C 'per':180C 'php':7A,21B,50B,87C,298C 'place':132C 'potenti':94C 'prior':103C,108C,113C,119C 'process':51B,84C,88C 'quadrat':38B,208C 'regist':337C 'repeat':124C,253C 'request':290C,340C 'rest':199C 'restrict':285C 'run':176C,184C 'scalar':145C,187C 'scan':174C 'second':54B,91C 'sent':314C 'sequenc':139C,239C 'servic':12A,60B,99C 'sever':131C 'similar':252C 'singl':288C 'size':41B,211C 'small':43B,76C 'space':178C 'stall':6A 'symfoni':1A,22B,24B,62C,101C,267C,328C 'symfony/yaml':23B 'tag':173C 'take':80C 'time':34B,160C,206C,230C,304C 'trigger':251C 'type':295C,319C 'unauthent':289C 'untrust':258C 'valid':308C 'version':102C 'well':228C 'work':125C,254C 'worker':8A,299C 'x':107C,112C,118C 'yaml':2A,4A,26B,45B,63C,70C,259C,276C,293C,309C,317C,332C,339C","nicknames":[],"mitigations":[],"who_affected":"Any PHP application that parses untrusted YAML is affected with default flags. In Symfony 7.4 and later, endpoints using #[MapRequestPayload] are exposed when the Yaml component is installed and acceptFormat is not restricted. In Symfony 6.4, exposure requires the application to register a yaml request format.","tier":"B","verified":{},"analyst_revisit_at":null,"fix_status":"available","audience":"developers","plain_action":null,"pkeys":[],"ptokens":[],"labels":["high","maprequestpayload","package","php","symfony","symfonyyaml"],"campaign_type":null,"search_a":"'-123792':15A,18A '-2026':14A,17A 'caus':9A 'craft':3A 'cve':13A,16A 'denial':10A 'document':5A 'php':7A 'servic':12A 'stall':6A 'symfoni':1A 'worker':8A 'yaml':2A,4A","search_b":"'busi':52B 'caus':57B 'compon':27B 'craft':44B 'denial':58B 'document':30B,46B 'exponenti':36B 'grow':35B 'ineffici':31B 'input':40B 'keep':48B 'maprequestpayload':19B 'minut':56B 'packag':20B 'pars':28B,33B 'php':21B,50B 'process':51B 'quadrat':38B 'second':54B 'servic':60B 'size':41B 'small':43B 'symfoni':22B,24B 'symfony/yaml':23B 'time':34B 'yaml':26B,45B","search_c":"'0':250C '5.4.56':105C '6':106C '6.4':329C '6.4.50':110C '7':111C '7.4':268C '7.4.23':115C '8':117C '8.1.11':121C 'accept':331C 'acceptformat':286C 'affect':261C 'alreadi':128C 'also':218C 'anchor':248C 'append':146C 'applic':336C 'blank':244C 'block':216C 'busi':89C,300C 'case':326C 'caus':95C 'charact':181C 'code':256C 'collect':153C,191C,202C,325C 'compon':64C,277C 'construct':234C 'consum':225C 'content':294C,318C 'copi':196C,219C 'craft':77C 'default':264C 'denial':97C 'depth':166C 'disproportion':81C 'document':71C,78C,306C 'done':129C 'embed':134C 'empti':238C 'endpoint':282C 'enough':321C 'everi':144C 'execut':303C 'exponenti':162C 'flag':265C 'flow':138C,190C,324C 'follow':241C 'format':341C 'grow':161C,207C 'includ':272C 'ineffici':72C 'inlin':65C 'input':214C 'instal':279C 'item':240C 'json':305C,312C 'keep':85C,296C 'key':171C 'later':270C 'level':223C 'line':245C 'long':82C 'map':135C,170C 'maprequestpayload':273C,330C 'match':169C,193C 'max':302C 'memori':226C 'minut':93C 'name':249C 'nest':154C,165C,215C,222C 'pars':68C,141C,159C,205C,257C 'parser':67C,123C 'pattern':168C 'payload':313C 'per':180C 'php':87C,298C 'place':132C 'potenti':94C 'prior':103C,108C,113C,119C 'process':84C,88C 'quadrat':208C 'regist':337C 'repeat':124C,253C 'request':290C,340C 'rest':199C 'restrict':285C 'run':176C,184C 'scalar':145C,187C 'scan':174C 'second':91C 'sent':314C 'sequenc':139C,239C 'servic':99C 'sever':131C 'similar':252C 'singl':288C 'size':211C 'small':76C 'space':178C 'symfoni':62C,101C,267C,328C 'tag':173C 'take':80C 'time':160C,206C,230C,304C 'trigger':251C 'type':295C,319C 'unauthent':289C 'untrust':258C 'valid':308C 'version':102C 'well':228C 'work':125C,254C 'worker':299C 'x':107C,112C,118C 'yaml':63C,70C,259C,276C,293C,309C,317C,332C,339C","first_public_at":"2026-11-04T11:43:34+00:00","kev":null,"cvss_vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/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":"596c5446-0ce5-4ba2-aa66-48b3b757a647","poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-123792","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-123792","severity":null,"published_at":"2026-11-06T16:17:55+00:00","modified_at":"2026-11-06T16:17:55+00:00","first_seen_at":"2026-11-06T16:42:41+00:00","fetched_at":"2026-11-06T16:42:41+00:00","note":null}],"documents":[{"id":87937,"url":"https://github.com/symfony/symfony/commit/08db22d52e5d3e6ec2f5c50db30a4d818100ffb9","title":"Patch: github.com","kind":"other","source":"nvd","publisher":"vendor","text":null,"published_at":null,"relation":"fix","confidence":null,"note":"Patch: github.com"},{"id":87938,"url":"https://github.com/symfony/symfony/commit/487f63bf2cacebc8ed8273c5c10d92955acd2402","title":"Patch: github.com","kind":"other","source":"nvd","publisher":"vendor","text":null,"published_at":null,"relation":"fix","confidence":null,"note":"Patch: github.com"},{"id":87939,"url":"https://github.com/symfony/symfony/commit/49e03035eda3000e978a4612db74900013255ccd","title":"Patch: github.com","kind":"other","source":"nvd","publisher":"vendor","text":null,"published_at":null,"relation":"fix","confidence":null,"note":"Patch: github.com"},{"id":87940,"url":"https://github.com/symfony/symfony/security/advisories/GHSA-hwfg-qwvh-2wfx","title":"Vendor advisory: github.com","kind":"vendor","source":"nvd","publisher":"vendor","text":null,"published_at":"2026-11-04T11:43:34+00:00","relation":"advisory","confidence":null,"note":"Vendor advisory: github.com"}],"exploit_sources":[],"notice":"Free to read, with fair use of about 60 pages a minute. For higher limits or API access: sales@infrastack.ai"}