CVE-2026-85077

Sanic allows CRLF injection in headers, causing response splitting hijacks.

• CVSS 8.2
• 113
• Input Validation and Sanitization
• Remote

Sanic is an opensource python web server/framework. Prior to version 24.12.1, and in version 25.12.0, the HTTP/1.1 response pipeline in sanic/response/types.py serializes response header names and values without rejecting carriage-return or line-feed characters. Applications that place attacker-controlled data in response.headers, file(…, filename=…), or cookie path and domain attributes can therefore emit injected headers and may split responses. Depending on application and proxy behavior, this can enable session fixation through injected cookies, cache poisoning, or security-header corruption. This issue is fixed in versions 24.12.1 and 25.12.1.

CVE

CVE-2026-85077

CWE

113

CVSS base score

8.2

Published

2026-09-17

OWASP

A03 Injection

Orthogonal defect classification

Checking

Code defect classification

Missing Check

Category

Input Validation and Sanitization

Subcategory

Insecure Parsing or Deserialization

Accessibility scope

Remote

Impact

Unauthorized Access

Affected component

Sanic

Fixed by upgrading

Yes

Solution

Upgrade Sanic to version 24.12.1 or later (or 25.12.1 or later).

from sanic import Sanic, response

app = Sanic(__name__)

@app.get("/test")
async def test(request):
    user_input = request.args.get("msg", "")
    # VULNERABLE: header injection
    resp = response.text("OK", headers={"X-User": user_input})
    return resp

from sanic import Sanic, response

app = Sanic(__name__)

@app.get("/test")
async def test(request):
    user_input = request.args.get("msg", "")
    # FIX: strip CRLF
    user_input = user_input.replace("\r", "").replace("\n", "")
    resp = response.text("OK", headers={"X-User": user_input})
    return resp

__VAITP_MODEL_REFUSED__

@misc{vaitp:cve202685077,
  title        = {{Sanic allows CRLF injection in headers, causing response splitting hijacks.}},
  author       = {Bogaerts, Fr\'ed\'eric and Ivaki, Naghmeh and Fonseca, Jos\'e},
  year         = {2026},
  note         = {VAITP Python Vulnerability Dataset, entry CVE-2026-85077},
  howpublished = {\url{https://netpack.pt/vaitp/vulnerability/CVE-2026-85077/}}
}