Web Developer for Chrome v0.4.9 Malicious Backdoor Supply Chain Compromise
Web Developer for Chrome v0.4.9 contained malicious code that generated a domain via a DGA and fetched a remote script. The fetched script conditionally loaded follow-on modules that performed extensive ad substitution and malvertising, displayed fake “repair” alerts that redirected users to affiliate programs, and attempted to harvest credentials when users logged in. Injected components enumerate common banner sizes for substitution, replace third-party ad calls, and redirect victim traffic to affiliate landing pages. Potential impacts include user-level code execution in the browser context, large-scale ad fraud and traffic hijacking, credential theft, and exposure to additional payloads delivered by the actor. The compromise was reported on by the maintainer of Web Developer for Chrome on August 2, 2017 and remediated in v0.5.0.
- Published
- Oct 8, 2025
- Updated
- Jun 16, 2026
- EPSS
- 0.5% · 43th percentile
- CWE
- CWE-506
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Report tools
Action score
37
Monitor
Low priority for now.
- CVSS
- 37 / 40 · 9.3 / 10
- CISA KEV
- 0 / 30 · Not listed
- EPSS
- 0 / 30 · 0.5%
CISA SSVC decision
- Exploitation
- proof of concept
- Automatable
- no
- Technical impact
- total
Vulnrichment: CISA's decision-tree inputs.
CNA vs NVD score
- NVD
- —
- CNA · VulnCheck
- 9.3
- NVD has not scored this yet; the score shown is the CNA’s.
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:N/SC:H/SI:H/SA:N
The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.
Affected systems
—
Versions reported by the vendor
Affected version ranges reported by the assigning authority (VulnCheck). Independent of NVD's CPE analysis and usually ahead of it.
Web Developer for Chrome Web Developer for Chrome
- 0.4.9affected
Remediation
Which version to upgrade to
Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.
No fix version is recorded for this entry. Check the references for vendor advisories.
Exploit status
No known public exploit
No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.
Research context
For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.
Timeline
From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.
No dated events beyond publication.
FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).
Patch and commit links
Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.
No commit or PR link among the references.
Credits
All researchersFinders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.
No credits in the CNA record.
Variant candidates
Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.
No nightly-computed relations.
Chain candidates
An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.
—
Bug bounty scope
No known public program.
Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).
Technical details
Attack conditions
- Anyone who can reach it over the internet can trigger it.
- No account or password is required.
- No special conditions are required; it is repeatable.
If successful
- Confidentiality
- Integrity
- Availability
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- A
- Scope
- X
Weakness class (CWE)
CWE-506 · Embedded Malicious CodeCVSS vector
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:N/SC:H/SI:H/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-secondary
Attack context
MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.
Attack patterns (CAPEC)
ATT&CK techniques
- Data Obfuscation: SteganographyT1001.002
- Obfuscated Files or Information: SteganographyT1027.003
- Obfuscated Files or Information: Compile After DeliveryT1027.004
- Obfuscated Files or Information: Embedded PayloadsT1027.009
- Supply Chain Compromise: Compromise Software Dependencies and Development ToolsT1195.001
- Supply Chain Compromise: Compromise Software Supply ChainT1195.002
- Signed Binary Proxy Execution: Compiled HTML FileT1218.001
- Template InjectionT1221
Noroxi analysis
No Noroxi analysis for this record yet
We don't hand-write analysis for all 385,000+ vulnerabilities; that wouldn't be honest. For notable, high-impact vulnerabilities our team writes the mechanism, detection and remediation steps.
We use this product, ask for helpChange log
No changes recorded on tracked fields yet. Score, KEV, exploit maturity and fix status changes appear here.
References
- chromewebstore.google.com/detail/web-developer/bfbameneiokkgbdmiekhjnmfkcnldhhm?pli=1
- gist.github.com/piedpiperRichard/076516da60f45842f1a6e6ae35a9a240/
- ui.vision/blog/chrome-extension-adware/
- web.archive.org/web/20170803163618/https://chrispederick.com/blog/web-developer-for-chrome-compromised/
- www.proofpoint.com/us/threat-insight/post/threat-actor-goes-chrome-extension-hijacking-spree
- www.vulncheck.com/advisories/web-developer-for-chrome-malicious-backdoor-supply-chain-compromise
Vendor advisories and official records. Exploit/PoC links are deliberately left out.