CVE-2026-8390Disclosure(mozilla / firefox)

MEDIUMCVSS 7.3 · HIGH

Exploit discussion active in current signal (2 latest mentions)

Immediate actions

Patch mozilla firefox systems immediately
Hunt for exploitation attempts and persistence artifacts
Increase monitoring for publicly documented tradecraft

Recommended action window: High priority (within 72h)

NVD description

Use-after-free in the JavaScript: WebAssembly component. This vulnerability was fixed in Firefox 150.0.3.

mozilla CVEs Back to dashboard

4.0/ 10 priority

Sources & remediation

Vendor / third-party advisories

https://www.mozilla.org/security/advisories/mfsa2026-45/

Other references

Weakness type (CWE)

CWE-416CWE-825

Priority

MEDIUM

Exploitation

NONE

PoC

YES

Patch

AVAILABLE

Momentum

STABLE

Are you affected?

If you run products in this scope, you should treat this CVE as relevant to your environment.

firefox

Threat summary

Public PoC and exploit tooling are both present
Patch or workaround signal is available
6 mentions across 4 observed days
Momentum state: stable

What's happening

Exploit tool or code specified in 1 signal
PoC mentioned or linked in 1 signal
Patch or workaround mentioned in 4 signals
Technical details provided in 4 signals
Disclosure: 2 classified signals
Peaked 3d ago at 2 mentions (2026-05-12); latest day: 2
6 total mentions across 4 days

Affected systems

Vendors

mozilla

Products

firefox

Deep dive

Activity timeline6 mentions / 4d

Signal classification4 categories

Disclosure

233.3%

Patch

233.3%

PoC

116.7%

General

116.7%

Referenced assets12 URLs

By indicator

Classification over time

Date	Total	Labels

2026-05-12	2	Disclosure1Patch1
2026-05-18	1	PoC1
2026-06-22	1	Patch1
2026-06-23	2	Disclosure1General1

Full discourse6 posts

情報の灯台@joho_no_todai108d
Patch
OpenAIとTrail of Bitsが共同で立ち上げたPatch the Planet。初回5日間のスプリントで19のOSSプロジェクトから数百件のバグを発見し、64件のプルリクエストを送った。 GPT-5.5が見つけたFirefoxの脆弱性（CVE-2026-8390）はPwn2Own Berlin開催の2日前にMozillaがパッチを適用し、登録6チーム中5チームが撤退している。 AIが穴を見つける速度に、直す手が追いついていない。報告を積むだけでなく、研究者がパッチまで仕上げてメンテナーに届ける設計が成果を出し始めた。 https://joho-todai.com/openai-daybreak-expansion-vulnerabilities-shortage/
Post summary
OpenAI’s GPT-5.5 uncovered CVE-2026-8390 in Firefox, which Mozilla patched two days before the Pwn2Own Berlin event; as a result, most competing teams withdrew.
0501532.0K
11.4K followersView on X
xvonfers@xvonfers149d
Disclosure
(CVE-2026-8390)[2038081]UAF in WASM https://hg-edge.mozilla.org/mozilla-central/rev/c4e56be1fb8eb25484f5663277ae00315dc7dc5a https://www.mozilla.org/en-US/security/advisories/mfsa2026-45/#CVE-2026-8390 Reported by OpenAI Preparedness, Bill Demirkapi
Post summary
CVE-2026-8390, a use‑after‑free in WebAssembly, has been disclosed with a source‑code reference and an associated Mozilla advisory indicating a patch is available.
021796.0K
5.0K followersView on X
Awesome Agents@awagents107d
General
OpenAI's GPT-5.5-Cyber found CVE-2026-8390 in Firefox's WebAssembly engine before Pwn2Own Berlin - five of six registered exploit entries withdrew. #Openai #Security Link in the first comment 👇 https://t.co/tJ2Q2newj8
Post summary
The post announces that OpenAI’s analysis discovered CVE-2026-8390 in Firefox’s WebAssembly engine before the Pwn2Own event, but offers no PoC, exploit code, active exploitation evidence, patch information, or detailed technical details.
1001064
841 followersView on X
Awesome Agents@awagents107d
Disclosure
New podcast episode: AI Patched Firefox Before Pwn2Own - OpenAI's Security Pivot OpenAI's GPT-5.5-Cyber found CVE-2026-8390 in Firefox's WebAssembly engine before Pwn2Own Berlin - five of six registered exploit entries withdrew. Full episode in the reply. #AI #Podcast https://t.co/v6qCmfcfjb
Post summary
The tweet announces that OpenAI’s AI tool identified CVE‑2026‑8390 in Firefox’s WebAssembly engine ahead of the Pwn2Own Berlin contest, but offers no PoC, exploit, or patch information.
1000063
841 followersView on X
dbugs@ptdbugs143d
PoC
Use-after-free in the JavaScript: WebAssembly component CVE: CVE-2026-8390 PT ID: PT-2026-40022 Vendor: Mozilla Product: Firefox CVSS: n/a Credits: OpenAI Preparedness, Bill Demirkapi Description: Use-after-free in the JavaScript: WebAssembly component. This vulnerability was fixed in Firefox 150.0.3. References: • https://dbugs.ptsecurity.com/vulnerability/CVE-2026-8390 • https://bugzilla.mozilla.org/show_bug.cgi?id=2038081 • https://www.mozilla.org/security/advisories/mfsa2026-45/ PoC/Exploit: https://github.com/kiddo-pwn/ffffirefox #dbugs_vuln
Post summary
CVE-2026-8390 is a use‑after‑free flaw in Firefox’s WebAssembly JavaScript component, for which a PoC is publicly available and a patch was released in Firefox 150.0.3.
01000300
1.2K followersView on X
White Rabbitx 🏴‍☠️@TheRabbitPy149d
Patch
🧨 Firefox 150.0.3 is a critical patch. Here's an overview: CVE‑2026‑8401 – sandbox escape in Profile Backup CVE‑2026‑8391 – priv‑esca‑like “other” JS engine bug CVE‑2026‑8390 – UAF in JS:WebAssembly CVE‑2026‑8389 – JIT miscompilation in JS JIT CVE‑2026‑8388 – wrong boundary checks in JS JIT Any one of these can pop your browser; together they’re a browser‑pwn trifecta. #Firefox #CVE‑2026‑8401 #CVE‑2026‑8391 #CVE‑2026‑8390 #CVE‑2026‑8389 #CVE‑2026‑8388 #BrowserSecurity #JIT #WebAssembly #JavaScript #DevSecOps https://nvd.nist.gov/vuln/detail/CVE-2026-8401 https://nvd.nist.gov/vuln/detail/CVE-2026-8391 https://nvd.nist.gov/vuln/detail/CVE-2026-8390 https://nvd.nist.gov/vuln/detail/CVE-2026-8389 https://nvd.nist.gov/vuln/detail/CVE-2026-8388
Post summary
Mozilla released Firefox 150.0.3 to patch five critical JavaScript and WebAssembly vulnerabilities (CVE‑2026‑8401 to CVE‑2026‑8388) with no active exploitation or PoC details reported.
0001082
1.3K followersView on X

CPE platform detail1 entries

Part:

Vendor:

Product:

Version:

Target SW:

Target HW:

1 of 1 entries

Part	Vendor	Product	Version	Target SW	Target HW
App	mozilla	firefox	-	-	-

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What researchers are saying

CVE-2026-8390

情報の灯台[verified]@joho_no_todaiPatch

OpenAI’s GPT-5.5 uncovered CVE-2026-8390 in Firefox, which Mozilla patched two days before the Pwn2Own Berlin event; as a result, most competing teams withdrew.

Awesome Agents[verified]@awagentsGeneral

The post announces that OpenAI’s analysis discovered CVE-2026-8390 in Firefox’s WebAssembly engine before the Pwn2Own event, but offers no PoC, exploit code, active exploitation evidence, patch information, or detailed technical details.

Awesome Agents[verified]@awagentsDisclosure

The tweet announces that OpenAI’s AI tool identified CVE‑2026‑8390 in Firefox’s WebAssembly engine ahead of the Pwn2Own Berlin contest, but offers no PoC, exploit, or patch information.

dbugs[verified]@ptdbugsPoC

CVE-2026-8390 is a use‑after‑free flaw in Firefox’s WebAssembly JavaScript component, for which a PoC is publicly available and a patch was released in Firefox 150.0.3.

White Rabbitx 🏴‍☠️[verified]@TheRabbitPyPatch

Mozilla released Firefox 150.0.3 to patch five critical JavaScript and WebAssembly vulnerabilities (CVE‑2026‑8401 to CVE‑2026‑8388) with no active exploitation or PoC details reported.

xvonfers@xvonfersDisclosure

CVE-2026-8390, a use‑after‑free in WebAssembly, has been disclosed with a source‑code reference and an associated Mozilla advisory indicating a patch is available.