CVE-2023-36807

PyPDF2 vulnerable to possible Infinite Loop when reading malformed objects

    else:
        # number object OR indirect reference
        peek = stream.read(20)
        stream.seek(-len(peek), 1)  # reset to start
        if IndirectPattern.match(peek) is not None:
            return IndirectObject.read_from_stream(stream, pdf)
        else:
            return NumberObject.read_from_stream(stream)

    elif tok in b"0123456789+-.":
        # number object OR indirect reference
        peek = stream.read(20)
        stream.seek(-len(peek), 1)  # reset to start
        if IndirectPattern.match(peek) is not None:
            return IndirectObject.read_from_stream(stream, pdf)
        else:
            return NumberObject.read_from_stream(stream)
    else:
        raise PdfReadError(
            f"Invalid Elementary Object starting with {tok} @{stream.tell()}"
        )

An attacker who uses this vulnerability can craft a PDF which leads to an infinite loop.
This infinite loop blocks the current process and can utilize a single core of the CPU by 100%. It does not affect memory usage. That is, for example, the case if the user extracted metadata from such a malformed PDF.

CVE-2023-36807 has a CVSS score of 6.2 (Medium). The vector is requires local access, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2.10.6); upgrading removes the vulnerable code path.

Kodem intelligence

Already deployed Kodem?

The issue was fixed with https://github.com/py-pdf/pypdf/pull/1331

1. What is CVE-2023-36807? CVE-2023-36807 is a medium-severity security vulnerability in PyPDF2 (pip), affecting versions = 2.10.5. It is fixed in 2.10.6.
2. How severe is CVE-2023-36807? CVE-2023-36807 has a CVSS score of 6.2 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of PyPDF2 are affected by CVE-2023-36807? PyPDF2 (pip) versions = 2.10.5 is affected.
4. Is there a fix for CVE-2023-36807? Yes. CVE-2023-36807 is fixed in 2.10.6. Upgrade to this version or later.
5. Is CVE-2023-36807 exploitable, and should I be worried? Whether CVE-2023-36807 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2023-36807 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2023-36807? Upgrade PyPDF2 to 2.10.6 or later.

Other vulnerabilities in PyPDF2