Bug 2543245 (CVE-2026-97689)

Summary: CVE-2026-97689 urllib3: urllib3: Denial of Service via unbounded memory allocation in chunk parser
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: high Docs Contact:
Priority: high    
Version: unspecifiedCC: blitton, cahl, dschmidt, ikhan, jdobes, jholecek, jlanda, jmitchel, jwong, kaycoth, kgaikwad, kshier, ljawale, mbarnett, msilmser, omaciel, orabin, rbobbitt, simaishi, stcannon, ttakamiy, yguenane, zzhou
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in urllib3. This flaw allows a Denial of Service (DoS) through unbounded memory allocation when parsing chunk-encoded responses. A malicious server can send an excessively long chunk-size line without a newline, exhausting client memory and terminating the application.
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Description OSIDB Bzimport 2026-09-29 15:52:23 UTC 
urllib3 is an HTTP client library for Python. From 1.10.3 until 2.8.0, the HTTPResponse.read_chunked and HTTPResponse.stream methods can allocate unbounded memory because the streaming chunk parser buffers the chunk-size field until newline or EOF without a length bound. The trigger is that a malicious server returns Transfer-Encoding: chunked followed by a very long run of bytes without a newline. The attack mechanism is that a malicious HTTP server sends a very long unterminated chunk-size line. The impact is that unbounded memory allocation can exhaust the client process. This issue is fixed in version 2.8.0.