VulnerabilityPublished 23 Oct 2026Updated 9 Nov 2026

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

Affects fastapiSource 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 0.142.3 when convenient.

Data as of 9 Nov 2026, 20:03 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

Patch: Available – fixed in 0.142.3

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 9 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 fastapi to 0.142.3.

Affected software

Product	Affected	Fixed in
Homebrewfastapi`pkg:brew/fastapi`Other threats	Affected >=0.142.0 <0.142.3	Fixed in 0.142.3

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

AI-suggested

A patch is available in fastapi version 0.142.3 that fixes this issue. Users should upgrade to this version or later to remediate the vulnerability. Until patched, limiting the maximum allowed size of tracestate headers at the HTTP server or proxy level may reduce exposure. Note that some servers already reject very large headers, but others accept very large tracestate headers, so relying solely on server limits is insufficient.

Description

A regular expression inefficiency in OpenTelemetry Python's TraceState.from_header method causes quadratic CPU time when parsing large tracestate headers with long runs of spaces or tabs. This can lead to significant processing delays and blocking of other connections in asynchronous servers. The issue affects versions from 1.0.0 through 1.45.0 and was fixed in version 0.142.3 of the related fastapi package. The vulnerability allows an unauthenticated attacker to cause denial of service by sending a specially crafted large tracestate header.

Impact

This vulnerability causes a denial of service condition by consuming excessive CPU resources during parsing of maliciously crafted tracestate headers. It can block the handling worker for multiple seconds, effectively causing service degradation or unavailability in asynchronous server environments. There is no direct confidentiality or integrity impact. The vulnerability is exploitable by unauthenticated attackers sending large tracestate headers.

Summary

The OpenTelemetry Python package's TraceState.from_header method uses a regular expression to split the inbound W3C tracestate header that begins with an unbounded optional whitespace run and lacks a length limit. This causes the regex engine to exhibit O(N²) CPU complexity when processing a long run of spaces or tabs not followed by a comma. The 32-member limit on tracestate keys is enforced only after splitting, so it does not prevent this inefficiency. As a result, a single unauthenticated request with a ~100 KB tracestate header can keep the handling worker busy for 6 to 12 seconds, blocking other connections in asyncio servers. The issue is present from version 1.0.0 through at least v1.45.0 and was fixed in fastapi version 0.142.3. Some HTTP servers limit header size and may mitigate the impact, but others accept very large headers, allowing exploitation. The sibling baggage propagator has a length check that tracestate lacks.

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Affected software

Description

AI analysisMachine-generated, updated 9 Nov 2026, 20:03 UTC

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