CVE-2020-15904 is a high-severity (CVSS 7.8) Out-of-bounds Write vulnerability in bsdiff4. A fix is available for bsdiff4 — see the affected versions and patch details below.
bsdiff4 out-of-bounds write via patch file
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
bsdiff4Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
A buffer overflow in the patching routine of bsdiff4 before 1.2.0 allows an attacker to write to heap memory (beyond allocated bounds) via a crafted patch file.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | bsdiff4 | all versions | 1.2.0pip install --upgrade 'bsdiff4==1.2.0' |
Affected Products
bsdiff4pypiDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for bsdiff4, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update bsdiff4 to 1.2.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-15904 is resolved across your whole dependency graph.
Workarounds
Constrain what reaches the vulnerable code: limit the size and shape of untrusted input, isolate the affected component in a sandboxed or least-privileged process, and enable the platform's memory-safety mitigations (ASLR, stack protector, hardened allocator) so an out-of-bounds access is more likely to fail closed than to be exploitable.
Frequently Asked Questions
Is CVE-2020-15904 in your dependencies?
Find it across PyPI, including transitive dependencies.