CVE-2018-1000656

The Pallets Project flask version Before 0.12.3 contains a CWE-20: Improper Input Validation vulnerability in flask that can result in Large amount of memory usage possibly leading to denial of service. This attack appear to be exploitable via Attacker provides JSON data in incorrect encoding. This vulnerability appears to have been fixed in 0.12.3. NOTE: this may overlap CVE-2019-1010083.

Published: 2018-08-20 Last update: 2026-06-17 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2018-1000656 is rated Moderate Risk (64.3/100): CVSS High severity, with medium exploitation likelihood (EPSS 3.85%). EPSS rose +3.27% over the last day, indicating growing attacker interest. Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2018-1000656

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.58% 3.85% +3.27%
2 2026-03-04 0.43% 0.58% +0.15%
3 2026-03-01 — 0.43% —

Full EPSS history (49 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2018-1000656

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.5 3.0 HIGH
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 3.6 [email protected]
5.0 2.0 MEDIUM
AV:N/AC:L/Au:N/C:N/I:N/A:P Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:N)
No confidentiality impact.
Integrity impact (I:N)
No integrity impact.
Availability impact (A:P)
Partial availability impact.
 10.0 2.9 [email protected]

Weakness enumeration for CVE-2018-1000656

GitHub Security Advisory for CVE-2018-1000656

GHSA-562c-5r94-xh97 · Severity: high · Ecosystem: pip — Flask is vulnerable to Denial of Service via incorrect encoding of JSON data

OS Trackers for CVE-2018-1000656

vendor priority summary link
debian not yet assigned CVE-2018-1000656 not yet assigned priority: Debian including 1 source packages (flask), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2018-1000656
redhat low — https://access.redhat.com/security/cve/CVE-2018-1000656
suse low CVE-2018-1000656 severity low: SUSE including 9 source package names (python-Flask, python2-Flask, …), 22 product×package rows across 14 product lines (HPE Helion OpenStack 8, SUSE Enterprise Storage 7, … (14 product lines)): Known Not Affected 13, Fixed 6, Will Not Fix 3. https://www.suse.com/security/cve/CVE-2018-1000656/
ubuntu low CVE-2018-1000656 low priority: Ubuntu including 1 source packages (flask), 8 status rows across 8 suites (bionic, cosmic, disco, eoan, focal, trusty, upstream, xenial): not-affected 4, released 4. https://ubuntu.com/security/CVE-2018-1000656

Affected software / configurations for CVE-2018-1000656

Vendor Product Version Raw CPE
palletsprojects flask < 0.12.3 cpe:2.3:a:palletsprojects:flask:*:*:*:*:*:*:*:*
netapp active_iq — cpe:2.3:a:netapp:active_iq:*:*:*:*:*:*:*:*
netapp hyper_converged_infrastructure — cpe:2.3:a:netapp:hyper_converged_infrastructure:*:*:*:*:*:*:*:*
netapp ontap_select_deploy_utility — cpe:2.3:a:netapp:ontap_select_deploy_utility:*:*:*:*:*:*:*:*

References for CVE-2018-1000656

cvelogic Threat Intelligence