CVE-2026-78207

Exploitation

Assessed, none found. CISA's assessment recorded neither public exploit code nor evidence of exploitation when it was made.

SSVC decision

• ExploitationnoneCISA recorded no public exploit code and no evidence of exploitation.
• AutomatableyesAn attacker can reliably automate reconnaissance through exploitation, so this scales.
• Technical ImpacttotalSuccessful exploitation gives total control of the vulnerable component.

CISA publishes the decision points, not a final SSVC decision. The decision also depends on mission and well-being impact, which is a property of your deployment rather than of the vulnerability.

EPSS probability

0.60% probability of exploitation activity in the next 30 days.

EPSS percentile

Equal to or higher than the score of 48.6% of scored records. A rank, not a probability.

NVD base score

9.3 (CVSS v4.0), scored by the NVD independently of the CNA.

NVD CVSS vector

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

NVD analysis status

Deferred. NVD last modified this record on 2026-10-14.

Red Hat severity

No Red Hat rating. Red Hat rates the CVEs that affect its products.

Exploit-prediction scores from FIRST. Independent scoring and analysis status from the NVD. Vendor severity from Red Hat. Exploitation assessment and catalog membership from CISA.

Published

2026-08-24 00:30Z2 MO AGO

Last updated

2026-08-29 11:47Z2 MO AGO

Reserved

2026-08-24

Assigning CNA

VulnCheck

Record state

PUBLISHED

Severity

Critical (CVSS 9.3)

CNA CVSS vector

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

Weaknesses

• CWE-1321Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')Variant

Data version

5.2

Document digest

bc78096c07c00e37fa189a0adaae207c1214734ce0245d88c8b3c00f6460c2b2

• github.comhttps://github.com/exceljs/exceljsproduct
• github.comGitHub Security Advisory (GHSA-qwr4-7h29-chpf)https://github.com/mateocallec/exceljs-hardened/security/advisories/GHSA-qwr4-7h29-chpfthird-party-advisory
• github.comhttps://github.com/exceljs/exceljs/blob/v4.4.0/lib/utils/under-dash.js#L155-L181technical-description
• www.vulncheck.comVulnCheck Advisory: exceljs through 4.4.0 Prototype Pollution via deepMerge Reached From Note Serializationhttps://www.vulncheck.com/advisories/exceljs-through-prototype-pollution-via-deepmerge-reached-from-note-serializationthird-party-advisory