VulnerabilityPublished 23 Oct 2026Updated 3 Nov 2026

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

Affects fastmcpSource GCVE Database

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Authoritative record:CVE-2026-114603· Medium 5.3

Not known to be exploited · CVSS 5.3 Medium : upgrade to 4.1.0 when convenient.

Data as of 3 Nov 2026, 22:58 UTC

CVSS 3.1 base score

5.3Medium

How severe the flaw is on the 0–10 CVSS scale.

Thin evidence

One scorer or none

CVSS scores by source
CNA (GitHub_M)	CVSS 3.1	5.3

EPSS: 0.4% chance of exploitation in 30 days – higher than 41% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 4.1.0

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: Low

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the impacted component are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 22 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 3 Nov 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade fastmcp to 4.1.0.

Affected software

Product	Affected	Fixed in
Homebrewfastmcp`pkg:brew/fastmcp`Other threats	Affected >=2.14.0 <4.1.0	Fixed in 4.1.0

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

A fix is available in opentelemetry-api version 4.1.0. Users should upgrade to version 4.1.0 or later to resolve this vulnerability. Until upgrading, users may consider limiting the maximum allowed size of tracestate headers at the server or proxy level to prevent excessively large headers from reaching the vulnerable parser. The sibling baggage propagator includes a length check that could serve as a model for mitigation. No other specific mitigations are indicated by the vendor advisory.

Description

CVE-2026-114603 is a vulnerability in the OpenTelemetry Python package opentelemetry-api affecting versions from 2.14.0 up to but not including 4.1.0. The issue arises from the TraceState.from_header method, which parses the W3C tracestate header using a regular expression with an unbounded optional-whitespace run and no length limit. This causes a quadratic time complexity (O(N²)) in CPU usage when processing specially crafted tracestate headers containing long runs of spaces or tabs without commas. An unauthenticated attacker can exploit this by sending a large tracestate header (~100 KB), causing significant CPU consumption and blocking server worker threads for several seconds. The vulnerability is mitigated in version 4.1.0 where the parsing logic is fixed.

Impact

An attacker can send a specially crafted tracestate header with a large number of spaces or tabs to cause the regex parser to consume CPU resources quadratically relative to the header size. This results in denial of service by blocking the handling worker for multiple seconds (e.g., ~6 seconds for 100 KB spaces, ~12 seconds for tabs). Under asyncio servers, this blocks other connections during that time, potentially degrading service availability. The vulnerability does not impact confidentiality or integrity but causes availability degradation due to CPU exhaustion.

Summary

The vulnerability exists in the opentelemetry-api Python package's TraceState.from_header method, which splits the inbound W3C tracestate header using a regular expression pattern that starts with an unbounded optional whitespace run ([ \t]*). This pattern causes the regex engine to exhibit quadratic time complexity when processing long runs of spaces or tabs without commas, leading to excessive CPU consumption. The 32-member limit on tracestate keys is enforced only after the split, so it does not prevent the expensive regex operation. The sibling baggage propagator includes a length check that prevents similar issues, but tracestate parsing lacks such a guard. The issue affects versions from 1.0.0 through at least 1.44.0 and 1.45.0, confirmed in main branch and tags, and is present in all versions from 2.14.0 up to but not including 4.1.0. Servers with permissive header size limits can be impacted, with some servers accepting very large tracestate headers, exacerbating the problem. The fix is included in version 4.1.0.

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Description

AI analysisMachine-generated, updated 3 Nov 2026, 21:34 UTC

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