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GHSA-jrpm-956j-96jg
org.http4s/http4s-ember-core_3org.http4s/http4s-ember-core_2.13org.http4s/http4s-ember-core_3Summary
Ember's chunk decoder parses the size token leniently: it strips leading and trailing whitespace and accepts a leading + or - sign. RFC9112 §7.1 defines chunk-size = 1*HEXDIG. An intermediary that parses the chunk boundary differently (or rejects it) will disagree with Ember on request framing, enabling HTTP request smuggling (TE.TE).
Impact
Server
Request smuggling (TE.TE) when ember-server is an origin behind an intermediary that forwards the body verbatim but interprets the malformed chunk sizes differently
- Front-end security bypass: the smuggled request reaches paths the intermediary might have blocked, with attacker-chosen method and headers.
- Cache poisoning: the smuggled response is associated with the next request key in a caching proxy.
- Request queue hijack:
Client
ember-client has the same leniencies on the response path, which enables response smuggling when http4s is used as a gateway. This is less severe, as it requires a malicious or compromised upstream rather than an anonymous remote client.
Preconditions
- Unauthenticated remote attacker (server)
- ember-server as origin behind a keep-alive intermediary
- Malicious or compromised upstream (client)
- Intermediary or upstream forwards chunked bodies without re-encoding and disagrees with Ember on
+prefix,-prefix, or leading and trailing octets rather than rejecting.
Workarounds
- Intermediary strictly rejects malformed chunk sizes
- Intermediary buffers and re-encodes request bodies
References
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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 does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability. The vulnerability can affect other systems as well, not just the initial system. There is a low impact on the confidentiality of the information. There is a low impact on the integrity of the data.
Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.
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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