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GHSA-75c5-xw7c-p5pm
No affected components available
Summary
The wrong string if check is run for iss checking, resulting in "acb" being accepted for "_abc_".
Details
This is a bug introduced in version 2.10.0: checking the "iss" claim
changed from isinstance(issuer, list) to isinstance(issuer, Sequence).
- if isinstance(issuer, list):
+ if isinstance(issuer, Sequence):
if payload["iss"] not in issuer:
raise InvalidIssuerError("Invalid issuer")
else:
Since str is a Sequnce, but not a list, in is also used for string
comparison. This results in if "abc" not in "__abcd__": being
checked instead of if "abc" != "__abc__":.
PoC
Check out the unit tests added here: https://github.com/jpadilla/pyjwt-ghsa-75c5-xw7c-p5pm
issuer = "urn:expected"
payload = {"iss": "urn:"}
token = jwt.encode(payload, "secret")
# decode() succeeds, even though `"urn:" != "urn:expected". No exception is raised.
with pytest.raises(InvalidIssuerError):
jwt.decode(token, "secret", issuer=issuer, algorithms=["HS256"])
Impact
I would say the real world impact is not that high, seeing as the signature still has to match. We should still fix it.
The vulnerability can be exploited over the network without needing physical access. It is difficult for an attacker to exploit this vulnerability and may require special conditions. An attacker needs high-level or administrative privileges. No user interaction is needed for the attacker to exploit this vulnerability. The impact is confined to the system where the vulnerability exists. There is a low impact on the integrity of the data.
Limited exploitation activity has been observed. Close monitoring and planned remediation are recommended.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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