CVE-2026-46384

iskorotkov/avro is a fast Go Avro codec. Prior to 2.33.0, several Avro decoder paths read attacker-controlled 64-bit values from the wire format and either narrowed them to platform-sized int before bounds-checking, or summed them with overflow-prone signed-int arithmetic. On 32-bit targets (GOARCH=386, arm, mips, wasm, etc.), the truncation paths can silently bypass byte-slice limits, select the wrong union branch, or hit the OCF negative-make panic via wrap. Three sub-issues are not 32-bit-specific: cumulative-size arithmetic overflow in arrayDecoder.Decode / mapDecoder.Decode / mapDecoderUnmarshaler.Decode (wraps at math.MaxInt64 on amd64 / arm64 and bypasses MaxSliceAllocSize / MaxMapAllocSize), math.MinInt negation in block-header handling, and make([]byte, size) with a negative size in OCF block reads — all three panic or bypass caps on any platform, giving an attacker a denial-of-service primitive there. This vulnerability is fixed in 2.33.0.

Several Avro decoder paths read attacker-controlled 64-bit values from the wire format and either narrowed them to platform-sized int before bounds-checking, or summed them with overflow-prone signed-int arithmetic. On 32-bit targets, the truncation paths can silently bypass byte-slice limits, select the wrong union branch, or hit a negative-make panic via wrap. Three sub-issues are not 32-bit-specific: cumulative-size arithmetic overflow in array and map decoders, negation of MinInt in block-header handling, and negative size in block reads. All three panic or bypass caps on any platform, giving an attacker a denial-of-service primitive. Exploitation requires only an untrusted Avro stream.

# Integer Overflow in Avro Decoder ## Summary Several Avro decoder paths read attacker-controlled 64-bit values from the wire format and either narrowed them to platform-sized `int` before bounds-checking, or summed them with overflow-prone signed-`int` arithmetic. On 32-bit targets (`GOARCH=386`, `arm`, `mips`, `wasm`, etc.), the truncation paths can silently bypass byte-slice limits, select the wrong union branch, or hit the OCF negative-`make` panic via wrap. Three sub-issues are not 32-bit-specific: cumulative-size arithmetic overflow in `arrayDecoder.Decode` / `mapDecoder.Decode` / `mapDecoderUnmarshaler.Decode` (wraps at `math.MaxInt64` on amd64 / arm64 and bypasses `MaxSliceAllocSize` / `MaxMapAllocSize`), `math.MinInt` negation in block-header handling, and `make([]byte, size)` with a negative size in OCF block reads — all three panic or bypass caps on any platform, giving an attacker a denial-of-service primitive there. Exploitation requires only an untrusted Avro stream. No primitives reach beyond denial-of-service on current code paths; see the union-index discussion below for a caveat. ## Description Six call sites in the decoder accepted `int64` values from the Avro wire format and converted to `int` before validation. On a 32-bit build any wire value with magnitude `≥ 2³¹` truncates and the post-conversion value bears no useful relationship to the original. A value of `(1<<32) + 5` narrows to `5`; `1<<32` narrows to `0`; values just past `MaxInt32` narrow to large negatives. This is distinct from the existing `Config.MaxSliceAllocSize`, `Config.MaxByteSliceSize`, and the new `Config.MaxMapAllocSize` limits, because narrowing happens *before* the limit comparison — the limit sees the truncated value, not the original wire value, so the cap is bypassed. Three further sub-issues are not 32-bit-specific: - `arrayDecoder.Decode`, `mapDecoder.Decode`, and `mapDecoderUnmarshaler.Decode` summed attacker-controlled block lengths via `size += int(l)` and then checked `size > limit`. On amd64 / arm64 the running total wraps at `math.MaxInt64`; the post-wrap negative value passes the `> limit` check, and the decoder proceeds. Regression test: `TestDecoder_ArrayMultiBlockExceedsMaxInt` uses `math.MaxInt − 2` for the second block's count and a `MaxSliceAllocSize` of 13 to demonstrate this on amd64. The Avro block-count field is a signed `long` on the wire, so block counts up to `math.MaxInt64` are admissible — there is no implicit 2³¹ ceiling. - `ReadBlockHeader()` returns the absolute value of negative block lengths; the negation is unsafe for `math.MinInt`, which on every platform panics on overflow. - `ocf/ocf.go readBlock()` passes the decoded block size directly to `make([]byte, size)`. A negative wire value panics on every platform; on 32-bit, values `> MaxInt32` additionally panic via the narrowing path. ## Affected components | File | Function(s) | Bug class | Platforms | |------|-------------|-----------|-----------| | `reader.go` | `ReadBlockHeader` — narrowing | Narrowing | 32-bit | | `reader.go` | `ReadBlockHeader` — `-math.MinInt` | Signed overflow (CWE-191) | all | | `reader.go` | `readBytes` (via `Reader.ReadBytes`, `Reader.ReadString`) | Narrowing | 32-bit | | `reader_skip.go` | `SkipString`, `SkipBytes` (and OCF skip path) | Narrowing | 32-bit | | `codec_array.go` | `arrayDecoder.Decode` | Cumulative-size arithmetic overflow (CWE-190) | all | | `codec_map.go` | `mapDecoder.Decode`, `mapDecoderUnmarshaler.Decode` | Cumulative-size arithmetic overflow (CWE-190) | all | | `ocf/ocf.go` | `skipToEnd`, `readBlock` — narrowing | Narrowing | 32-bit | | `ocf/ocf.go` | `readBlock` — negative `make([]byte, …)` | Unchecked-negative (CWE-1284) | all | | `reader_generic.go` | union-type index decoding in `Reader.ReadNext` | Narrowing, possible wrong-branch selection | 32-bit | PR #9 (commit [`bed99b3`](https://github.com/iskorotkov/avro/commit/bed99b315ec097a1a5eb7ae074ef57a91848c583)) covered `ReadBlockHeader`, the cumulative checks in array/map codecs, and the skip helpers. The completeness pass (commit [`e1a570f`](https://github.com/iskorotkov/avro/commit/e1a570f9a8a4fe4b1bc2b4b1fb6d24e4a5f04358)) covered the union index, `readBytes`, and OCF `readBlock`, and added a 32-bit CI job. Note: the typed-codec union decoder in `codec_union.go` (`getUnionSchema` → `Reader.ReadInt`) is **not** affected by the union-index narrowing — `ReadInt` returns `int32`, no narrowing occurs. The narrowing is specific to `Reader.ReadNext` in the generic decode path (reached via `Unmarshal` into `any` / `map[string]any`). ## Technical details 1. **Block-header narrowing and `MinInt` negation.** `ReadBlockHeader()` returned wire-format `int64` values through narrower operations; on 32-bit, large positives truncated. Negating `math.MinInt` to convert a negative block-count signal into a positive size is undefined-on-overflow, and on every platform `-MinInt` panics on overflow when used in subsequent arithmetic. The fix reads into a `*64`-suffixed local, range-checks against `MinInt32`/`MaxInt32` (or `MinInt`/`MaxInt` as appropriate), and narrows after validation. 2. **Cumulative array and map size overflow (all platforms).** `arrayDecoder.Decode`, `mapDecoder.Decode`, and `mapDecoderUnmarshaler.Decode` summed attacker-controlled block lengths using overflow-prone addition; cumulative size could wrap before reaching the configured limit. On amd64 with `MaxSliceAllocSize = 13`, block 1 of 3 elements, block 2 of `math.MaxInt − 2` elements: the pre-fix `size += int(l)` wraps to `math.MinInt`, then `MinInt > 13` is false, so the check passes and the decoder proceeds. The fix uses subtraction-safe comparisons (`l > limit - size` rather than `size + l > limit`), which is overflow-immune. 3. **Skip-length truncation.** `SkipString`, `SkipBytes`, and the OCF skip helper now route through `SkipNBytesInt64()`, which keeps the length as `int64` and range-checks before any narrowing. 4. **Byte-slice length truncation.** A wire-format length such as `(1<<32) + 5` truncated to `5` in `readBytes()`, slipping past `Config.MaxByteSliceSize` on 32-bit. The fix reads the length as `int64`, compares against `MaxByteSliceSize` before narrowing, and returns "value is too big" if exceeded. 5. **Union index narrowing (generic decode path only).** `Reader.ReadNext` decoded the union index as `int64` and immediately cast to `int`. On 32-bit, `1<<32` narrowed to `0` and silently selected `types[0]` despite the explicit upper-bound check immediately above. If `types[0]` is the null branch (idiomatic for `["null", T]` nullable unions), the practical result is a null value where the producer encoded a non-null payload — a DoS-grade logic error. If `types[0]` is a non-trivial schema, downstream bytes are parsed against the wrong schema and produce well-typed but semantically wrong values; treat this as the worst-case interpretation when assessing impact on your own deployment. The typed-codec union decoder (`codec_union.go` `getUnionSchema` → `Reader.ReadInt`) is not affected. 6. **OCF block-size narrowing and negative `make`.** `readBlock()` passes the decoded `int64` size directly to `make([]byte, size)`. A negative wire value panics on every platform; a value `> MaxInt32` additionally panics via the 32-bit narrowing path. The fix validates the size is in `[0, MaxByteSliceSize]` before narrowing. ## Fixed behavior Both commits apply the same pattern across every site: 1. Read the wire value into an `int64`-typed local. 2. Range-check upper and lower bounds before narrowing. 3. Compare cumulative limits using subtraction-safe arithmetic. 4. Route skip operations through `SkipNBytesInt64()`. 5. Return descriptive errors using the consistent `"value is too big"` / `"value is too small"` wording. 6. Cast to `int` only after validation succeeds. CI: a `test-386` job runs the suite under `GOARCH=386` with `CGO_ENABLED=0` (`-race` is amd64/arm64-only). Three tests with untyped `2147483648` constants whose `t.Skipf` gates fire too late (the file fails to compile before any test runs) were split into sibling `*_64bit_test.go` files gated by `//go:build amd64 || arm64 || ...`. ## Affected versions - `github.com/hamba/avro/v2` — all versions up to and including `v2.31.0` (repository is read-only upstream). - `github.com/iskorotkov/avro/v2` — all versions prior to `v2.33.0`. ## Fixed versions `github.com/iskorotkov/avro/v2` `v2.33.0` and later. There is no upstream fix for `github.com/hamba/avro/v2` — module path is archived. Migrate to the fork as described under Mitigation. ## Mitigation Migrate from `github.com/hamba/avro/v2` to `github.com/iskorotkov/avro/v2 >= v2.33.0`. The packages share the same API surface; replace the import path and run `go mod tidy`: ```diff - import "github.com/hamba/avro/v2" + import "github.com/iskorotkov/avro/v2" ``` For consumers that prefer the original import path, a `replace` directive in `go.mod` is supported: ``` replace github.com/hamba/avro/v2 => github.com/iskorotkov/avro/v2 v2.33.0 ``` `replace` is honoured only for the **main** module of a build — transitive consumers must add their own `replace`, or migrate the import path directly. No further configuration is required to benefit from the integer-narrowing fixes — the validation runs on the existing decode path. If you cannot upgrade immediately: - Do not decode untrusted Avro data on any platform — the cumulative-arithmetic overflow paths (`arrayDecoder.Decode`, `mapDecoder.Decode`, `mapDecoderUnmarshaler.Decode`) are reachable on amd64 / arm64. The truncation paths on 32-bit cannot be mitigated by setting `Config.MaxByteSliceSize` lower, because the truncated post-narrowing value is what the limit sees, not the original wire value. - For the cross-platform `math.MinInt` and OCF negative-size panic paths, wrapping `Decode` / OCF read calls in a goroutine with `defer recover()` contains the crash, but is not a substitute for upgrading. The other narrowing paths return errors rather than panicking, so `recover()` does nothing for them. - Isolate decoding workers so a crash is bounded. ## Proof-of-concept inputs - A `bytes` or `string` length of `(1<<32) + N` for small `N`, which narrows to `N` on 32-bit and bypasses `Config.MaxByteSliceSize`. - A union index of `1<<32`, which narrows to `0` on 32-bit and selects `types[0]` despite the upper-bound check. - An array or map encoded across multiple blocks whose cumulative element count wraps the signed `int` running total before the limit check fires. Demonstrated on amd64 by `TestDecoder_ArrayMultiBlockExceedsMaxInt`: `MaxSliceAllocSize = 13`, block 1 of `3`, block 2 of `math.MaxInt − 2`. Wraps to `math.MinInt`, check passes, decoder proceeds. - A block header whose absolute value is `math.MinInt`, triggering the unsafe negation (cross-platform). - An OCF block size that is negative on the wire, causing `make([]byte, size)` to panic (cross-platform); or a positive value `> MaxInt32` on 32-bit, same outcome via narrowing. ## References - Initial hardening PR: [iskorotkov/avro#9](https://github.com/iskorotkov/avro/pull/9) - Completeness pass PR: [iskorotkov/avro#10](https://github.com/iskorotkov/avro/pull/10) - Fix commits: [`bed99b3`](https://github.com/iskorotkov/avro/commit/bed99b315ec097a1a5eb7ae074ef57a91848c583), [`e1a570f`](https://github.com/iskorotkov/avro/commit/e1a570f9a8a4fe4b1bc2b4b1fb6d24e4a5f04358) - Release: [`v2.33.0`](https://github.com/iskorotkov/avro/releases/tag/v2.33.0) - Security policy: [`SECURITY.md`](https://github.com/iskorotkov/avro/blob/main/SECURITY.md) - Related advisories on this fork: [`GHSA-w8j3-pq8g-8m7w`](https://github.com/iskorotkov/avro/security/advisories/GHSA-w8j3-pq8g-8m7w) (CPU exhaustion — overlaps via the same large-block-count payload shape), [`GHSA-mx64-mj3q-7prj`](https://github.com/iskorotkov/avro/security/advisories/GHSA-mx64-mj3q-7prj) (unbounded map allocation) - Cross-module precedent on `hamba/avro`: [`GO-2023-1930`](https://pkg.go.dev/vuln/GO-2023-1930) / `CVE-2023-37475` / `GHSA-9x44-9pgq-cf45` - Upstream (read-only): [`hamba/avro`](https://github.com/hamba/avro) ## Credits - **Discovery and initial fixes** (PR #9, commit `bed99b3` — `ReadBlockHeader`, cumulative array/map checks, skip helpers): Daniel Błażewicz ([@klajok](https://github.com/klajok)) - **Completeness fixes** (commit `e1a570f` — union index, `readBytes`, OCF `readBlock`, 32-bit CI coverage): Ivan Korotkov ([@iskorotkov](https://github.com/iskorotkov)) ## Timeline - **2026-05-04** — Initial integer-overflow hardening (PR #9, `bed99b3`) merged. - **2026-05-04** — Completeness pass (`e1a570f`) merged; 32-bit CI job added. - **2026-05-06** — `v2.33.0` tagged and released. - **2026-05-11** — Advisory published. - **2026-05-15** — Advisory revised.

iskorotkov/avro es un códec Avro rápido para Go. Antes de la versión 2.33.0, varias rutas del decodificador Avro leían valores de 64 bits controlados por el atacante del formato de transmisión y los reducían a un entero (int) del tamaño de la plataforma antes de la verificación de límites, o los sumaban con aritmética de enteros con signo propensa a desbordamientos. En objetivos de 32 bits (GOARCH=386, arm, mips, wasm, etc.), las rutas de truncamiento pueden eludir silenciosamente los límites de las porciones de bytes, seleccionar la rama de unión incorrecta o provocar el pánico 'negative-make' de OCF a través de un 'wrap'. Tres subproblemas no son específicos de 32 bits: desbordamiento aritmético de tamaño acumulativo en arrayDecoder.Decode / mapDecoder.Decode / mapDecoderUnmarshaler.Decode (se ajusta en math.MaxInt64 en amd64 / arm64 y elude MaxSliceAllocSize / MaxMapAllocSize), negación de math.MinInt en el manejo de encabezados de bloque, y make([]byte, size) con un tamaño negativo en las lecturas de bloques OCF - los tres provocan pánico o eluden los límites en cualquier plataforma, dando al atacante una primitiva de denegación de servicio allí. Esta vulnerabilidad se corrige en la versión 2.33.0.