EEF-CVE-2026-111101 CVE-2026-111101 GHSA-jwh3-j29h-qfmw
HTTP/1.1 chunked request bodies made of 1-byte chunks amplify memory use in Bandit
- Severity
- 0.0 / 10
- Unknown · CVSS 4.0
- Exploit chance (EPSS)
- 0.60%
- Chance of exploitation in the next 30 days. Higher than 48.83% of scored vulnerabilities.
- Known exploited
- No
- Not in CISA's catalog
- Weakness
- CWE-770 Allocation of Resources Without Limits or Throttling
- Fix
1.14.0- Upgrade bandit to this version or later
Description
Summary
Allocation of Resources Without Limits or Throttling vulnerability in the HTTP/1.1 chunked body reader of mtrudel bandit allows an unauthenticated remote attacker to exhaust server memory and CPU via a request body made of many 1-byte chunks.
The chunked reader in lib/bandit/http1/socket.ex keeps every chunk as its own list cell and binary term until IO.iodata_to_binary/1 joins them, and nothing limits the number of chunks. The :length option of read_body/2 counts only data bytes, so tiny chunks cost far more memory than their payload: 48 MB of 1-byte chunks grew one handler process to about 500 MB and took about 6 s of CPU. The route does not need to read the body, because on keep-alive connections ensure_completed/1 drains unread bodies through the same reader.
This issue affects bandit: from 0.1.0 before 1.14.0.
Details
1. Per-chunk accumulation. do_read_chunked_data! in lib/bandit/http1/socket.ex collects chunks as [body | chunk], adding a cons cell and a binary term for every chunk.
2. Byte-only limit. :length limits data bytes, not the number of chunks, so a body of 1\r\nx\r\n chunks becomes an 8-million-element improper list before IO.iodata_to_binary runs. Sending 48 MB of 1-byte chunks grew the handler heap to about 500 MB and used about 6 s of CPU. The same body as one 8 MB chunk peaked at about 16 MB and took 5 ms.
3. No body read needed. On keep-alive connections, ensure_completed/1 drains unread bodies through the same path. Against a Plug that never calls read_body, the attack used about 417 MB.
Proof of concept
- Run Bandit with a Plug that calls
Plug.Conn.read_body(conn, length: 1_000_000, read_length: 1_000_000). - Send
POST /withTransfer-Encoding: chunkedand a body of 1,000,000 chunks of1\r\nA\r\n, followed by0\r\n\r\n. - When
read_bodyreturns the 1,000,000 body bytes, the handler process holds about 48 MB and BEAM memory has grown by about 55 MB, for 6 MB sent.
Impact
An unauthenticated client can make a single HTTP/1.1 request hold many times its body size in server memory (about 48 MB for a 1 MB body in the reporter's test), and keep CPU busy while the chunks are joined. This affects any Bandit server that accepts HTTP/1.1 requests, whether or not its routes read the body.
Workarounds
From 0.7.0, a server whose clients and proxies all speak HTTP/2 can disable HTTP/1 with http_1_options: [enabled: false], so that the vulnerable chunked body reader never runs.
Affected versions
Hex
| Package | Vulnerable | Fixed in |
|---|---|---|
| bandit | >= 0.1.0, < 1.14.0 |
1.14.0 |
How to fix
Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.
bandit Hex → 1.14.0
- mix
{:bandit, "~> 1.14.0"} # then: mix deps.update bandit
Severity breakdown
CVSS 4.0 0.0
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
- Attack vector
- Network
- Attack complexity
- Low
- Attack requirements
- None
- Privileges required
- None
- User interaction
- None
- Confidentiality (vulnerable system)
- None
- Integrity (vulnerable system)
- None
- Availability (vulnerable system)
- High
- Confidentiality (subsequent systems)
- None
- Integrity (subsequent systems)
- None
- Availability (subsequent systems)
- None
Weakness
CWE-770: Allocation of Resources Without Limits or Throttling
The product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated.
How to prevent it
- Requirements: Clearly specify the minimum and maximum expectations for capabilities, and dictate which behaviors are acceptable when resource allocation reaches limits.
- Architecture and Design: Limit the amount of resources that are accessible to unprivileged users. Set per-user limits for resources. Allow the system administrator to define these limits. Be careful to avoid CWE-410.
- Architecture and Design: Design throttling mechanisms into the system architecture. The best protection is to limit the amount of resources that an unauthorized user can cause to be expended. A strong authentication and access control model will help prevent such attacks from occurring in the first place, and it will help the administrator to identify who is committing the abuse. The login application should be protected against DoS attacks as much as possible. Limiting the database access, perhaps by caching result sets, can help minimize the resources expended. To further limit the potential for a DoS attack, consider tracking the rate of requests received from users and blocking requests that exceed a defined rate threshold.
- Implementation: Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
- Architecture and Design: For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.
- Architecture and Design: Mitigation of resource exhaustion attacks requires that the target system either: recognizes the attack and denies that user further access for a given amount of time, typically by using increasing time delays uniformly throttles all requests in order to make it more difficult to consume resources more quickly than they can again be freed. The first of these solutions is an issue in itself though, since it may allow attackers to prevent the use of the system by a particular valid user. If the attacker impersonates the valid user, they may be able to prevent the user from accessing the server in question. The second solution can be difficult to effectively institute -- and even when properly done, it does not provide a full solution. It simply requires more resources on the part of the attacker.
- Architecture and Design: Ensure that protocols have specific limits of scale placed on them.
- Architecture and Design, Implementation: If the program must fail, ensure that it fails gracefully (fails closed). There may be a temptation to simply let the program fail poorly in cases such as low memory conditions, but an attacker may be able to assert control before the software has fully exited. Alternately, an uncontrolled failure could cause cascading problems with other downstream components; for example, the program could send a signal to a downstream process so the process immediately knows that a problem has occurred and has a better chance of recovery. Ensure that all failures in resource allocation place the system into a safe posture.
- Operation, Architecture and Design: Use quotas or other resource-limiting settings provided by the operating system or environment. For example, when managing system resources in POSIX, setrlimit() can be used to set limits for certain types of resources, and getrlimit() can determine how many resources are available. However, these functions are not available on all operating systems. When the current levels get close to the maximum that is defined for the application (see CWE-770), then limit the allocation of further resources to privileged users; alternately, begin releasing resources for less-privileged users. While this mitigation may protect the system from attack, it will not necessarily stop attackers from adversely impacting other users. Ensure that the application performs the appropriate error checks and error handling in case resources become unavailable (CWE-703).
References
Advisories
Fixes and patches
Packages
Other links
Timeline
- Published
- Last updated by the source
- Latest EPSS score
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| EEF-CVE-2026-116078 HTTP/2 request bodies made of 1-byte DATA frames amplify memory use in Bandit | Not rated yet | Also affects bandit |
| EEF-CVE-2026-108529 SETTINGS and stream-0 WINDOW_UPDATE frames trigger quadratic work over blocked streams in Bandit | Not rated yet | Also affects bandit |
| EEF-CVE-2026-110499 Client-chosen HPACK encoder table size is applied uncapped, growing per-connection state with every response in Bandit | Not rated yet | Also affects bandit |
| EEF-CVE-2026-109584 HTTP/2 cookie crumb join expands a small HPACK header block into an unbounded allocation in Bandit | Not rated yet | Also affects bandit |
| EEF-CVE-2026-111103 HTTP/2 StreamError recovery rolls back connection state and bypasses per-connection limits in Bandit | Not rated yet | Also affects bandit |
| EEF-CVE-2026-113436 Quadratic bignum parsing of Content-Length and Host port values in Bandit | Not rated yet | Also affects bandit |
| EEF-CVE-2026-110314 WebSocket frames keep reaching the WebSock after a server-initiated close in Bandit | Not rated yet | Also affects bandit |
| EEF-CVE-2026-114213 WebSocket 1-byte continuation frames bypass `max_fragmented_message_size` in Bandit | Not rated yet | Also affects bandit |
Credits: Jonatan Männchen / EEF, Mat Trudel, Peter Ullrich
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