What is CVE-2026-18503?

CVE-2026-18503 is Super-linear CPU usage for unbounded input to csv.Sniffer.sniff(). The supplied enrichment data classifies it as Remote Code Exec mapped to CWE-1176 CWE-1176.

Which versions are affected?

Affected product and version evidence is listed in the product table above. Current public advisories should be checked for exact version scope before patch targeting is finalized.

Is there active exploitation?

Active exploitation is not confirmed from current sources for CVE-2026-18503. If exploitation is not confirmed from current sources, teams should document that status and continue monitoring KEV, vendor, and telemetry updates.

No. CVE-2026-18503 is not listed in CISA KEV in the supplied enrichment data. KEV status should be monitored because it can change after initial disclosure or after exploitation becomes publicly confirmed.

Is there a public exploit?

3 public PoC repositories reported; 0 marked weaponized in current dataset. Public exploit or PoC availability should raise triage priority, especially for exposed or business-critical systems.

How can defenders detect it?

Start with EDR process telemetry, host service logs where available. Look for vulnerability-class behavior, product errors, suspicious authentication events, exploit probes, and abnormal process activity based only on evidence that applies to the affected product.

How should teams prioritize it?

Prioritize CVE-2026-18503 using CVSS 2.4, EPSS 0%, KEV status, public PoC status, and asset exposure. Internet-facing, privileged, or business-critical deployments should be handled first.

Are workarounds available?

The supplied mitigation guidance says to apply vendor patches and restrict external exposure until fixed. Fixed-version evidence is listed in the mitigation section above.

Which threat actors are linked publicly?

No public threat actor linkage is confirmed from current sources. Do not attribute exploitation to a threat actor unless the source evidence explicitly supports that linkage.

What should be done in the next 24 hours?

Identify exposed assets running affected vendor/product/version combinations. Prioritize based on EPSS, PoC availability, and external exposure. Search available logs for exploit probes, errors, authentication anomalies, or suspicious child processes matching the vulnerability class. Open remediation tickets with affected assets, owners, evidence status, and detection coverage so decisions are traceable.

lowRemote Code Execpublic exploit

CVE-2026-18503

CVE-2026-18503 — Super-linear CPU usage for unbounded input to csv.Sniffer.sniff()

Attacker-controlled CSV samples can trigger super-linear regular-expression work during dialect sniffing and consume significant CPU when applications pass unbounded input to csv.Sniffer.sniff().

Published Aug 10, 2026Updated Aug 10, 2026Sources: NVD, Python Software Foundation (CNA), GitHub, GitHub Security Advisory, SOCRadar CTI

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the scoring sources call it.

Exploitation

Exploit code

public exploit, none observed

EPSS

ahead of 0% of scored CVEs

Affects

Python Software Foundation

3 products listed

CVSS base

2.4

low

Remediation

The vendor's own words where we have them.

Upgrade CPython to a fixed release. Apply vendor patches per advisory and restrict external exposure of the affected component until patched.

First 24 hours

Ordered from the record's own fields — exposure first, because you cannot patch what you have not found.

Identify exposed assets running affected vendor/product/version combinations.
Prioritize based on EPSS, PoC availability, and external exposure.
Search available logs for exploit probes, errors, authentication anomalies, or suspicious child processes matching the vulnerability class.

Affected scope

Vendor, product and version as the advisories word them.

Vendor	Product	Versions	Status
Python Software Foundation	CPython	0 to < 3.13.15	Vulnerable
Python Software Foundation	CPython	3.14.0 to < 3.14.7	Vulnerable
Python Software Foundation	CPython	3.15.0a1 to < 3.15.0rc1	Vulnerable

Every base score collected

Sources score independently and disagree; each row says who scored it and under which version.

Score	Version	Severity	Expl.	Impact	Source
2.4	CVSS 4.0	low	—	—	Python Software Foundation (CNA)

CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:P/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N

What this weakness leads to

MITRE's own consequences and mitigations for the weakness class — the authority's wording, not guidance derived from the CVSS vector.

MITRE

CWE-1176 · Inefficient CPU Computation

DoS: Resource Consumption (CPU)
Reduce Performance::

Weakness & attack patterns

CWE-1176

Inferred from the weakness class — not observed against this CVE.

CAPEC-242 · Code InjectionCAPEC-35 · Leverage Executable Code in Non-Executable Files

Public exploit

Capability, not use: code existing is a different claim from anyone running it.

Repositories

Detection

Read off the CVSS vector and the weakness class. Starting points, not rules we have tested.

Monitor for scanner or exploit-pattern traffic after 3 public PoC repositories were reported.

EDR process telemetryhost service logs

Timeline

What happened to this CVE, newest first — with the readings a source repeats on a schedule counted underneath rather than listed.

2026
Added · CVSS 3.1 2.4
Aug 10, 2026 · NVD
Initial · CVE published
Aug 10, 2026 · NVD
Added · GHSA-2345-wr3r-cxf2 published (low)
Aug 10, 2026 · GitHub Security Advisory

References

9 on the record

github.com/python/cpython/commit/063d4555c94ef412c731527dbf30193327f2ee82
Exploit, Third Party Advisory
github.com/python/cpython/commit/476fb09cdb0d73e645849d98c610e7e5697ce7c9
Exploit, Third Party Advisory
github.com/python/cpython/commit/89f29c760c02774b099ddd6863268eb13fa3946a
Exploit, Third Party Advisory
github.com/python/cpython/commit/b30c7fa9edd921a118f286e9f90f560777fa693b
Exploit, Third Party Advisory
github.com/python/cpython/issues/98820
Exploit, Third Party Advisory
github.com/python/cpython/pull/153694
Exploit, Third Party Advisory
mail.python.org/archives/list/[email protected]/thread/KQ7NBMCPAZJHRROQXJQE4GMXGLD5KHBS/
Vendor Advisory
nvd.nist.gov/vuln/detail/CVE-2026-18503
NVD

Elsewhere on this site

Python Software Foundationevery CVE for this vendor
Remote Code Execsame class
CWE-1176other pages naming this weakness

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record1

What should defenders know first?

CVE-2026-18503 is Super-linear CPU usage for unbounded input to csv.Sniffer.sniff(), a low vulnerability affecting CPython from Python Software Foundation. The current evidence does not list it in CISA KEV, and the exploit status is: Active exploitation is not confirmed from current sources for CVE-2026-18503. Public exploit evidence is: 3 public PoC repositories reported; 0 marked weaponized in current dataset. The affected-version evidence is listed in the key facts and affected products tables. Defenders should first verify whether exposed or business-critical assets run those versions, then apply vendor patches or mitigations, restrict reachable attack surface, and preserve logs for detection review. CVSS 2.4 describes technical severity, while EPSS 0% helps estimate near-term exploit likelihood; neither replaces asset context. Unknown fields should remain explicit in tickets, and threat actor, IOC, victimology, or payload claims should not be added unless a cited source supports them. Monitor CISA KEV, vendor advisories, NVD changes, public PoC repositories, and internal telemetry for update triggers.