Security: Unbounded memory consumption when buffering S3 object streams#312
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`getObject` converts the entire S3 response stream into a Buffer via `streamToBuffer` with no size limit. Large objects can exhaust Lambda memory and cause denial of service if object size is attacker-influenced or not strictly controlled. Affected files: s3-service.js Signed-off-by: tuanaiseo <221258316+tuanaiseo@users.noreply.github.com>
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Pull request overview
Adds a size cap to the in-memory buffering performed by s3-service.getObject() to mitigate a potential DoS from very large S3 objects exhausting Lambda memory. The cap is configurable via AWS_S3_MAX_BUFFERED_OBJECT_SIZE / AWS_S3_MAX_OBJECT_SIZE env vars and defaults to 10 MiB. The previously-shared streamToBuffer import from ./utils is replaced by a local streamToBufferWithLimit helper that aborts mid-stream when the cap is exceeded.
Changes:
- Introduce a configurable
MAX_BUFFERED_OBJECT_SIZE(default 10 MiB) read from env vars. - Add a local
streamToBufferWithLimithelper that destroys the source stream and throws when the limit is exceeded. - In
getObject, pre-flight reject responses whoseContentLengthexceeds the limit, and enforce the limit mid-stream when reading the body.
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| const MAX_BUFFERED_OBJECT_SIZE = parseInt( | ||
| process.env.AWS_S3_MAX_BUFFERED_OBJECT_SIZE || | ||
| process.env.AWS_S3_MAX_OBJECT_SIZE || | ||
| 10485760, | ||
| 10 | ||
| ); |
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| const MAX_BUFFERED_OBJECT_SIZE = parseInt( | ||
| process.env.AWS_S3_MAX_BUFFERED_OBJECT_SIZE || | ||
| process.env.AWS_S3_MAX_OBJECT_SIZE || | ||
| 10485760, | ||
| 10 | ||
| ); |
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| const streamToBufferWithLimit = async (stream, maxSize) => { | ||
| const chunks = []; | ||
| let size = 0; | ||
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| for await (const chunk of stream) { | ||
| const buffer = Buffer.isBuffer(chunk) ? chunk : Buffer.from(chunk); | ||
| size += buffer.length; | ||
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| if (size > maxSize) { | ||
| if (typeof stream.destroy === 'function') stream.destroy(); | ||
| throw new Error('S3 object exceeds maximum allowed buffered size'); | ||
| } | ||
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| chunks.push(buffer); | ||
| } | ||
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| return Buffer.concat(chunks); | ||
| }; |
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| @@ -21,9 +45,18 @@ exports.getObject = (params) => { | |||
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| if (!res.Body) return res; | |||
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| if ( | |||
| Number.isFinite(MAX_BUFFERED_OBJECT_SIZE) && | |||
| MAX_BUFFERED_OBJECT_SIZE > 0 && | |||
| typeof res.ContentLength === 'number' && | |||
| res.ContentLength > MAX_BUFFERED_OBJECT_SIZE | |||
| ) { | |||
| throw new Error('S3 object exceeds maximum allowed buffered size'); | |||
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Problem
getObjectconverts the entire S3 response stream into a Buffer viastreamToBufferwith no size limit. Large objects can exhaust Lambda memory and cause denial of service if object size is attacker-influenced or not strictly controlled.Severity:
highFile:
lib/s3-service.jsSolution
Avoid full buffering for arbitrary objects. Enforce a maximum allowed content length before reading, stream directly to the client/storage when possible, and abort reads when size thresholds are exceeded.
Changes
lib/s3-service.js(modified)Testing