OpenTelemetry-Go is the Go implementation of OpenTelemetry. From version 1.10.0 until 1.33.0, the sdk/trace/span.go attribute truncation path can fail to enforce AttributeValueLengthLimit for string and string-slice attributes containing the valid Unicode replacement character U+FFFD. safeTruncateValidUTF8 treats the valid replacement rune as invalid UTF-8 and returns the original input, while strings.ToValidUTF8 leaves that valid rune unchanged, so a second safeTruncate attempt can also return the oversized value. An attacker who controls span attribute content can retain values longer than the configured limit, increasing per-span memory use and weakening denial-of-service protection in the instrumented process. This issue is fixed in version 1.33.0.

Affected: Go: go.opentelemetry.io/otel/sdk

### Summary

The OpenTelemetry Go SDK trace package can fail to enforce `AttributeValueLengthLimit` for string attributes containing the valid Unicode replacement character U+FFFD. An oversized attacker-controlled attribute value that includes U+FFFD is returned untruncated, bypassing the configured memory/DoS protection and allowing increased per-span memory usage. The finding is low severity because it requires a deployment with attribute value length limits enabled and attacker-controlled data being recorded into span attributes.

Introduced in commit 49a6536

### Details

String and string-slice span attributes are truncated through `safeTruncate` when `AttributeValueLengthLimit` is non-negative. The finding evidence identifies this enforcement path in `sdk/trace/span.go:303-331`, with string attributes passed to `safeTruncate` at `sdk/trace/span.go:309-310` and string-slice entries passed to `safeTruncate` in the loop beginning at `sdk/trace/span.go:312`.

`safeTruncate` first calls `safeTruncateValidUTF8`; if that returns `ok=false`, it calls `strings.ToValidUTF8(input, "")` and retries. The relevant code is identified in `sdk/trace/span.go:337-355`. `safeTruncateValidUTF8` treats any `utf8.RuneError` from `utf8.DecodeRuneInString` as invalid UTF-8 and immediately returns the original input with `ok=false`. However, Go also returns `utf8.RuneError` for a valid encoded U+FFFD rune. The validation artifact confirms this behavior with output `r=U+FFFD size=3 runeError=tru…

Affected: Ubuntu:22.04:LTS: golang-opentelemetry-otel, Ubuntu:24.04:LTS: golang-opentelemetry-otel, Ubuntu:26.04:LTS: golang-opentelemetry-otel

OpenTelemetry-Go is the Go implementation of OpenTelemetry. From version 1.10.0 until 1.33.0, the sdk/trace/span.go attribute truncation path can fail to enforce AttributeValueLengthLimit for string and string-slice attributes containing the valid Unicode replacement character U+FFFD. safeTruncateValidUTF8 treats the valid replacement rune as invalid UTF-8 and returns the original input, while strings.ToValidUTF8 leaves that valid rune unchanged, so a second safeTruncate attempt can also return the oversized value. An attacker who controls span attribute content can retain values longer than the configured limit, increasing per-span memory use and weakening denial-of-service protection in the instrumented process. This issue is fixed in version 1.33.0.