MinIO affected a DoS via Unbounded Memory Allocation in S3 Select CSV Parsing

### Impact _What kind of vulnerability is it? Who is impacted?_ MinIO's S3 Select feature is vulnerable to memory exhaustion when processing CSV files containing lines longer than available memory. The CSV reader's `nextSplit()` function calls `bufio.Reader.ReadBytes('\n')` with no size limit, buffering the entire input in memory until a newline is found. A CSV file with no newline characters causes the entire contents to be read into a single allocation, leading to an OOM crash of the MinIO server process. This is exploitable by any authenticated user with `s3:PutObject` and `s3:GetObject` permissions. The attack is especially practical when combined with compression: a ~2 MB gzip-compressed CSV can decompress to gigabytes of data without newlines, allowing a small upload to cause large memory consumption on the server. However, compression is not required , a sufficiently large uncompressed CSV with no newlines triggers the same issue. **Affected component:** `internal/s3select/csv/reader.go`, function `nextSplit()`. **CWE:** CWE-770 (Allocation of Resources Without Limits or Throttling) ### Affected Versions All MinIO releases are through the final release of the minio/minio open-source project. The vulnerability was introduced in commit https://github.com/minio/minio/commit/7c14cdb60e53dbfdad2be644dfb180cab19fffa7, which added S3 Select support for CSV. The CSV reader has used unbounded line reads since this commit (originally via Go's stdlib `encoding/csv.Reader`, later via `bufio.Reader.ReadBytes` after a refactor in [PR #8200](https://github.com/minio/minio/pull/8200). The first affected release is `RELEASE.2018-08-18T03-49-57Z`. ### Patches **Fixed in**: MinIO AIStor RELEASE.2025-12-20T04-58-37Z The fix replaces the unbounded `bufio.Reader.ReadBytes('\n')` call with a byte-at-a-time loop that caps line scanning at 128 KB (`csvSplitSize`). If no newline is found within this limit, the reader returns an error instead of continuing to buffer. #### Binary Downloads | Platform | Architecture | Download | | -------- | ------------ | --------------------------------------------------------------------------- | | Linux | amd64 | [minio](https://dl.min.io/aistor/minio/release/linux-amd64/minio) | | Linux | arm64 | [minio](https://dl.min.io/aistor/minio/release/linux-arm64/minio) | | macOS | arm64 | [minio](https://dl.min.io/aistor/minio/release/darwin-arm64/minio) | | macOS | amd64 | [minio](https://dl.min.io/aistor/minio/release/darwin-amd64/minio) | | Windows | amd64 | [minio.exe](https://dl.min.io/aistor/minio/release/windows-amd64/minio.exe) | #### FIPS Binaries | Platform | Architecture | Download | | -------- | ------------ | --------------------------------------------------------------------------- | | Linux | amd64 | [minio.fips](https://dl.min.io/aistor/minio/release/linux-amd64/minio.fips) | | Linux | arm64 | [minio.fips](https://dl.min.io/aistor/minio/release/linux-arm64/minio.fips) | #### Package Downloads | Format | Architecture | Download | | ------ | ------------ | ----------------------------------------------------------------------------------------------------------------------------------- | | DEB | amd64 | [minio_20251220045837.0.0_amd64.deb](https://dl.min.io/aistor/minio/release/linux-amd64/minio_20251220045837.0.0_amd64.deb) | | DEB | arm64 | [minio_20251220045837.0.0_arm64.deb](https://dl.min.io/aistor/minio/release/linux-arm64/minio_20251220045837.0.0_arm64.deb) | | RPM | amd64 | [minio-20251220045837.0.0-1.x86_64.rpm](https://dl.min.io/aistor/minio/release/linux-amd64

CVSS 4.0

CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Severity from

GitHub (reviewed advisory)

Weakness

CWE-770

Also known as

CVE-2026-39414, GO-2026-5415

• github.com/minio/minio/security/advisories/GHSA-h749-fxx7-pwpg
• nvd.nist.gov/vuln/detail/CVE-2026-39414
• github.com/minio/minio/pull/8200
• github.com/minio/minio/commit/7c14cdb60e53dbfdad2be644dfb180cab19fffa7
• docs.min.io/enterprise/aistor-object-store/upgrade-aistor-server/community-edition
• github.com/minio/minio
• pkg.go.dev/vuln/GO-2026-5415?q