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How the CVE Works (Technical Explanation)
The vulnerability resides in the `cryptography` library’s handling of non-contiguous Python buffers passed to APIs that accept buffer protocol objects (e.g., Hash.update()). A non-contiguous buffer, such as a reversed `bytes` object created via buf[::-1], does not store its data in a single, continuous block of memory. Instead, it is represented by a Python buffer structure containing references to disjoint memory segments, along with a logical length that can be less than the underlying allocated size.
When such a buffer is passed to a vulnerable API, the library’s internal C code iterates over the buffer’s data. Due to a flaw in how the buffer’s actual memory layout is interpreted, the code fails to correctly bound the read operations. Specifically, the C implementation uses the buffer’s logical length to control a loop that reads memory from the buffer’s underlying storage. However, because the storage for a non-contiguous buffer may be larger than the logical view, the loop can continue past the intended end of the data. This results in a classic out-of-bounds read, causing the program to read arbitrary data from adjacent memory addresses.
The issue is triggered on Python versions greater than 3.11, where the buffer protocol’s behavior for non-contiguous views differs from earlier versions. An example is Hash.update(buf[::-1]). The reversed view creates a non-contiguous memory layout. The vulnerable code, expecting a contiguous buffer, does not handle this layout, leading to an out-of-bounds read.
This flaw can lead to information disclosure (leaking sensitive memory contents) or, in some scenarios, a crash (denial of service). It can be exploited remotely if an attacker can control the buffer passed to these APIs, such as in applications that process untrusted input for hashing or other cryptographic operations. The affected versions are from `45.0.0` up to, but not including, 46.0.7. The fix is implemented in version `46.0.7` and later, which properly validates the buffer layout and correctly handles non-contiguous views.
DailyCVE Form
Platform: Python pip
Version: 45.0.0 to <46.0.7
Vulnerability : Buffer overflow
Severity: Medium (6.9)
date: 2026-04-08
Prediction: Already patched (2026-04-08)
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Analytics
Count vulnerable cryptography installations pip list | grep cryptography | grep -E "45.[0-9]+.[0-9]+" | wc -l Check for processes using the vulnerable library lsof | grep cryptography | wc -l Monitor for potential exploitation attempts in logs grep -i "cryptography|buffer overflow|cve-2026-39892" /var/log/.log
Exploit:
import hashlib from cryptography.hazmat.primitives import hashes from cryptography.hazmat.backends import default_backend Create a non-contiguous buffer (reversed view) data = b'A' 1024 non_contiguous = data[::-1] Vulnerable call to Hash.update() on Python >3.11 h = hashes.Hash(hashes.SHA256(), backend=default_backend()) h.update(non_contiguous) Out-of-bounds read occurs here digest = h.finalize()
Protection from this CVE
Upgrade to patched version pip install --upgrade cryptography==46.0.7 Verify installation python -c "import cryptography; print(cryptography.<strong>version</strong>)" For containerized environments, rebuild images with patched version docker run --rm python:3.12-slim bash -c "pip install cryptography==46.0.7"
Impact
- Confidentiality: High – Out-of-bounds read can leak sensitive memory contents
- Integrity: None – The vulnerability does not allow data modification
- Availability: Medium – May cause application crashes (denial of service)
- Remote Exploitation: Yes – If attacker can control input to hash functions
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Sources:
Reported By: github.com
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