Bug 2491466 (CVE-2026-53538)

Summary: CVE-2026-53538 python-multipart: Python-Multipart: Information disclosure due to parser differential in form data handling
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: alinfoot, anpicker, anthomas, aprice, bbrownin, bparees, dfreiber, dkeler, drow, dschmidt, dtrifiro, ebourniv, ehelms, ggainey, hasun, ilpinto, jburrell, jdobes, jfula, jlanda, jowilson, jpasqual, jsamir, juwatts, jwong, kaycoth, kshier, lgallett, ltomasbo, mbarnett, mhayden, mhulan, nmoumoul, nyancey, oezr, omaciel, ometelka, orabin, osousa, pcreech, prwatson, ptisnovs, rbryant, rchan, rjohnson, sbunciak, sdoran, simaishi, smallamp, stcannon, suppawar, syedriko, teagle, thason, tmalecek, ttakamiy, vkumar, weaton, xdharmai, yguenane, ykashtan
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in Python-Multipart, a tool used for processing web form data. A remote attacker could exploit a vulnerability where the software incorrectly interprets certain characters as separators in web form data. This difference in interpretation compared to standard web practices allows an attacker to bypass security checks and inject additional data fields. This could lead to unauthorized information disclosure.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Description OSIDB Bzimport 2026-06-22 18:03:03 UTC 
Python-Multipart is a streaming multipart parser for Python. Prior to 0.0.30, QuerystringParser treated ; as a field separator in application/x-www-form-urlencoded bodies, in addition to &. The WHATWG URL standard, modern browsers, and Python's urllib.parse (since the CVE-2021-23336 fix) treat only & as a separator. This creates a parser differential: the same bytes are tokenized into different fields than a WHATWG compliant intermediary would produce, allowing an attacker to smuggle extra form fields past an upstream body inspecting component. This vulnerability is fixed in 0.0.30.