{"id":"CVE-2026-116264","kind":"vulnerability","aliases":["CVE-2026-116264"],"related":[],"title":"Perl MIME::Parser: invalid Content-Type parameter hides multipart boundary from filters","description":"MIME::Field::ParamVal versions before 5.521 for Perl allow one invalid Content-Type parameter to hide the parameters after it, including the multipart boundary.\n\nParameter parsing stops at the first parameter whose name it cannot read, such as x:y=1 or a name containing an 8-bit byte, and drops every parameter after it. When the boundary is among them, MIME::Parser keeps the multipart body as a single undecoded part without marking the parse as ambiguous.\n\nMail readers that skip the invalid parameter still find the boundary. A remote sender can hide an attachment from a filter that relies on ambiguous_content() while the recipient's mail client shows it.","summary":"MIME::Field::ParamVal before 5.521 stops parsing Content-Type parameters at the first unreadable name, dropping the multipart boundary when it comes after. MIME::Parser then keeps the body as one undecoded part without flagging ambiguity, so a message can carry an attachment that a filter relying on ambiguous_content() does not see.","severity":"low","cvss":null,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["mail-filtering","mime-parser","package","perl"],"not_affected_if":["no-perl-mail-filter","versions-5.521-or-later"],"how_to_check":"- Check the installed MIME::Field::ParamVal version with `perl -MMIME::Field::ParamVal -e 'print $MIME::Field::ParamVal::VERSION'`\n- Look for code that calls `ambiguous_content()` on MIME::Parser results to decide whether to scan or block mail","fix":"- Upgrade MIME::Field::ParamVal to `5.521` or later\n- Until upgraded, treat mail with undecoded multipart bodies as suspicious in filters that depend on ambiguous_content()","status":"open","published_at":"2026-10-28T18:17:12+00:00","first_seen_at":"2026-10-28T18:34:33+00:00","triaged_at":"2026-10-28T18:35:32+00:00","updated_at":"2026-10-28T18:35:32+00:00","category":"package","confidence":0.6,"triage":{"at":"2026-10-28T18:35:32Z","model":"claude-haiku-5-5","output":{"fix":"- Upgrade MIME::Field::ParamVal to `5.521` or later\n- Until upgraded, treat mail with undecoded multipart bodies as suspicious in filters that depend on ambiguous_content()","reach":"internet","title":"Perl MIME::Parser: invalid Content-Type parameter hides multipart boundary from filters","impact":"medium","summary":"MIME::Field::ParamVal before 5.521 stops parsing Content-Type parameters at the first unreadable name, dropping the multipart boundary when it comes after. MIME::Parser then keeps the body as one undecoded part without flagging ambiguity, so a message can carry an attachment that a filter relying on ambiguous_content() does not see.","category":"package","nicknames":[],"who_cares":["perl","mail-filtering","mime-parser"],"confidence":0.6,"needs_auth":"no","worst_case":"Attachment hidden from content filter reaches recipient mail client","analyst_note":"Check the NVD entry and the upstream MIME-tools changelog for the exact fixed release and whether any other MIME parsers are affected.","how_to_check":"- Check the installed MIME::Field::ParamVal version with `perl -MMIME::Field::ParamVal -e 'print $MIME::Field::ParamVal::VERSION'`\n- Look for code that calls `ambiguous_content()` on MIME::Parser results to decide whether to scan or block mail","needs_analyst":true,"not_affected_if":["no-perl-mail-filter","versions-5.521-or-later"],"who_is_affected":"Teams running Perl mail-processing code that uses MIME::Parser and MIME::Field::ParamVal to scan or filter inbound messages, where a filter decision depends on ambiguous_content(). Mail clients and systems that do not use this Perl module are not exposed through this flaw, and the sources do not say whether other MIME parsers share the behavior.","user_interaction":"no","needs_special_setup":"unknown","severity_if_unknown":"low"},"cost_usd":0.000693,"input_tokens":3441,"output_tokens":698,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'-116264':16A,19A '-2026':15A,18A '1':123C '5.521':32B,87C '8':129C 'allow':90C 'ambigu':64B,77B,160C,185C 'among':142C 'attach':71B,178C 'bit':130C 'bodi':57B,149C 'boundari':11A,47B,106C,140C,171C 'byte':131C 'cannot':117C 'carri':69B 'client':192C 'come':50B 'contain':127C 'content':6A,36B,78B,94C,186C 'content-typ':5A,35B,93C 'cve':14A,17A 'drop':44B,133C 'everi':134C 'field':29B,83C 'filter':13A,22B,74B,181C 'find':169C 'first':41B,112C 'flag':63B 'hide':9A,98C,176C 'includ':103C 'invalid':4A,92C,166C 'keep':55B,146C 'mail':21B,161C,191C 'mail-filt':20B 'mark':156C 'messag':67B 'mime':2A,24B,28B,52B,82C,144C 'mime-pars':23B 'multipart':10A,46B,105C,148C 'name':43B,115C,126C 'one':59B,91C 'packag':26B 'paramet':8A,38B,96C,100C,107C,113C,135C,167C 'paramv':30B,84C 'pars':34B,108C,158C 'parser':3A,25B,53B,145C 'part':61B,154C 'perl':1A,27B,89C 'read':118C 'reader':162C 'recipi':189C 'reli':75B,183C 'remot':173C 'see':81B 'sender':174C 'show':193C 'singl':152C 'skip':164C 'still':168C 'stop':33B,109C 'type':7A,37B,95C 'undecod':60B,153C 'unread':42B 'version':85C 'whose':114C 'without':62B,155C 'x':121C 'y':122C","nicknames":[],"mitigations":[],"who_affected":"Teams running Perl mail-processing code that uses MIME::Parser and MIME::Field::ParamVal to scan or filter inbound messages, where a filter decision depends on ambiguous_content(). Mail clients and systems that do not use this Perl module are not exposed through this flaw, and the sources do not say whether other MIME parsers share the behavior.","tier":"C","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-10-28T18:17:12+00:00","kev":null,"cvss_vector":null,"cvss_by":null,"poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-116264","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-116264","severity":null,"published_at":"2026-10-28T18:17:12+00:00","modified_at":"2026-10-28T18:17:12+00:00","first_seen_at":"2026-10-28T18:34:33+00:00","fetched_at":"2026-10-28T18:34:33+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"}