CVE-2026-114603: OpenTelemetry Python · Unbounded tracestate parsing in opentelemetry-api

## Summary `TraceState.from_header` splits the inbound W3C `tracestate` header with a regular expression that starts with an unbounded optional-whitespace run, and no length limit is applied first. A run of spaces or tabs that is not followed by a comma costs O(N²) CPU. A single unauthenticated request with a ~100 KB `tracestate` keeps the handling worker busy for ~6 s (spaces) to ~12 s (tabs); under an asyncio server it blocks every other connection for that time. ## Affected component / version - Package: `opentelemetry-api` (pip) — `opentelemetry/trace/span.py` (`TraceState.from_header`), reached from `opentelemetry/trace/propagation/tracecontext.py` (`TraceContextTextMapPropagator.extract`). - Confirmed in `main` (5e8083e8) and in the v1.44.0 and v1.45.0 tags; the same pattern is present back to v1.0.0 (introduced by #1599, March 2021). Not exhaustively verified against every release in between. - Reachable with the default propagators (`OTEL_PROPAGATORS` defaults to `tracecontext,baggage`) from any server instrumentation that calls `propagate.extract()`, for example `opentelemetry-instrumentation-asgi`. ## Details 1. The header reaches the parser without any length check: ```python # opentelemetry-api/src/opentelemetry/trace/propagation/tracecontext.py:57 tracestate_headers = getter.get(carrier, self._TRACESTATE_HEADER_NAME) # <-- attacker-controlled request header(s), any size if tracestate_headers is None: tracestate = None else: tracestate = TraceState.from_header(tracestate_headers) # <-- no length check before parsing (line 61) ``` 2. The split pattern and the parser: ```python # opentelemetry-api/src/opentelemetry/trace/span.py:45 _TRACECONTEXT_MAXIMUM_TRACESTATE_KEYS = 32 # <-- only enforced later, in TraceState.__init__, after the split _delimiter_pattern = re.compile(r"[ \t]*,[ \t]*") # <-- (line 46) starts with an unbounded [ \t]* # span.py:382 @classmethod def from_header(cls, header_list: list[str]) -> TraceState: pairs = {} # type: dict[str, str] for header in header_list: members: list[str] = re.split(_delimiter_pattern, header) # <-- (line 400) VULNERABLE: O(N^2) on "a=b" + " " * N + "x" for member in members: if not member: continue match = _member_pattern.fullmatch(member) if not match: _logger.warning( # <-- also logs the entire malformed member (up to the whole header) "Member doesn't match the w3c identifiers format %s", member, ) return cls() ... ``` `re.split` tries the pattern at every offset. At each offset inside a whitespace run, `[ \t]*` consumes the rest of the run, finds no `,`, backtracks and fails, then the engine moves one character forward and repeats. N characters × up to N steps each = O(N²). The 32-member limit never gets a chance to run because `split` has to finish first. 3. The sibling propagator already has the missing guard: ```python # baggage/propagation/__init__.py:68 _MAX_HEADER_LENGTH = 8192 ... if len(header.encode()) > self._MAX_HEADER_LENGTH: # <-- (line 93) rejected before any regex runs; tracestate has no equivalent _logger.warning(...) return context ``` A 16 KiB header costs ≈ 0.25 s and an 8 KiB header ≈ 0.07 s. Measured cost of `extract()` on one core (valid `traceparent`, `tracestate: "a=b" + N spaces + "x"`): the time quadruples each time N doubles (see the proof of concept). Roughly 0.06 s at 10,000 characters, 1 s at 40,000, 4 s at 80,000, 9 s at 100,000 (tabs are about 1.6× slower). Whether a server lets such a header through (header-size limits, tested): gunicorn rejects ≥ 8190 bytes (response code 431); `uvicorn --http h11` rejects above 16 KiB (400); waitress accepts up to 256 KiB (200 KB accepted, 300 KB rejected); `uvicorn --http httptools` — the default parser with `uvicorn[standard]` — accepted 300 KB, 1 MB, 5 MB and 20 MB `tracestate` headers. ## Proof of concept ### A. Show the quadratic cost (no server needed) 1. Install the API: `pip install opentelemetry-api` (any version from 1.0 up to the current main is affected). 2. Save as `poc_tracestate.py`: ```python import logging import time from opentelemetry.trace.propagation.tracecontext import TraceContextTextMapPropagator # The library logs the whole malformed member at WARNING; silence it so the timings stay readable. logging.disable(logging.CRITICAL) TRACEPARENT = "00-0af7651916cd43dd8448eb211c80319c-b7ad6b7169203331-01" propagator = TraceContextTextMapPropagator() previous = None for n in (10_000, 20_000, 40_000, 80_000): # N spaces after a valid member, no comma anywhere in the header carrier = {"traceparent": TRACEPARENT, "tracestate": "a=b" + " " * n + "x"} start = time.perf_counter() propagator.extract(carrier) elapsed = time.perf_counter() - start growth = f"x{elapsed / previous

• github.com/open-telemetry/opentelemetry-python/security/advisories/GHSA-xcq7-p3pf-p88h (opens in a new tab)
• github.com/open-telemetry/opentelemetry-python/pull/5749 (opens in a new tab)
• github.com/open-telemetry/opentelemetry-python/commit/d5224bf4ffdf2aee1b592ad238dcc32ca957f26b (opens in a new tab)
• github.com/open-telemetry/opentelemetry-python (opens in a new tab)
• github.com/open-telemetry/opentelemetry-python/blob/main/CHANGELOG.md (opens in a new tab)
• github.com/open-telemetry/opentelemetry-python/releases/tag/v1.45.1 (opens in a new tab)

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