Skip to content

Do not crash on a JWT with a non-base64url signature (fixes #6101) #6102

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
chan770 wants to merge 1 commit into
base: master
Choose a base branch
from
+9 −1
Open

Do not crash on a JWT with a non-base64url signature (fixes #6101) #6102

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
10 changes: 9 additions & 1 deletion lib/utils/jwt.py
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -89,6 +89,8 @@ def crackHMAC(token, secrets, limit=None):
's3cr3t'
>>> crackHMAC(token, ["admin", "letmein"]) is None
True
>>> crackHMAC("eyJhbGciOiJIUzI1NiJ9.eyJ1c2VyIjoiYWRtaW4ifQ.x", ["secret"]) is None
True
"""

data = parseJWT(token)
Expand All @@ -97,7 +99,13 @@ def crackHMAC(token, secrets, limit=None):

fn = HMAC_ALGORITHMS[data["header"]["alg"].upper()]
signingInput = getBytes(data["signingInput"])
target = decodeBase64(data["signature"], binary=True)

try:
target = decodeBase64(data["signature"], binary=True)
except Exception:
# a signature segment that is not valid base64url (e.g. a truncated/malformed token that still
# matches the JWT pattern) cannot be an HMAC we could verify, so it is simply not crackable
return None

for index, secret in enumerate(secrets):
if limit is not None and index >= limit:
Expand Down