Description

January, the media proxy/embed service of stoatchat (stoatchat/stoatchat), before version 0.15.5 improperly resolves SVG <image href> values as local filesystem paths when a fetched resource is served as image/svg+xml. An unauthenticated remote attacker who causes the service to proxy an attacker-hosted SVG (e.g. via the /proxy endpoint) can determine whether local files exist through observable response-time differences, and can cause supported local image files to be disclosed after re-encoding. Because each referenced file is read in full with no effective limit on the number or total volume of reads, a single request can also generate an unbounded amount of local filesystem I/O and memory pressure (the published proof of concept drives about 4.34 GB of reads), leading to denial of service. The issue is fixed in 0.15.5.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "8.2",
  "pubDate": "2026-09-26T14:16:51.577Z",
  "pubdate": "2026-09-26T14:16:51.577Z",
  "executiveSummary": "The media proxy service in Stoatchat, version 0.15.5 and prior, contains a critical vulnerability regarding the improper resolution of SVG image href attributes. An unauthenticated remote attacker can exploit this flaw to perform unauthorized local filesystem access and file disclosure.\nThe vulnerability manifests when the service processes a maliciously crafted SVG image retrieved via the /proxy endpoint. By manipulating the <image href> tag, an attacker can force the application to treat local filesystem paths as external resources.\nThis flaw enables two primary attack vectors: information disclosure via side-channel analysis (response-time differentials) and a significant Denial of Service (DoS) condition caused by resource exhaustion. The application fails to validate file references or impose constraints on I/O operations, allowing an attacker to trigger unbounded reads of sensitive local files. The total volume of data processed during a single exploitation instance can exceed 4 GB, resulting in severe memory pressure and system-wide I/O performance degradation. Stoatchat users should prioritize upgrading to version 0.15.5 or later to remediate the underlying flaw.",
  "technicalDetails": "The vulnerability resides within the media proxy component of Stoatchat, which performs improper input validation when parsing and rendering SVG files identified as image/svg+xml. The root cause is a lack of path sanitization or restriction in the handling of the <image> element's 'href' attribute during the SVG rendering process.\nWhen the proxy fetches an attacker-controlled SVG, the underlying rendering engine processes the XML structure. By providing an 'href' attribute pointing to a local filesystem path (e.g., file:///etc/passwd or other sensitive image assets), the application inadvertently attempts to resolve and read the file from the local disk instead of a remote network host.\nThe exploitation flow is as follows: 1) An unauthenticated attacker submits a malicious SVG file to the publicly exposed /proxy endpoint. 2) The proxy service retrieves and attempts to parse this SVG. 3) Upon encountering an <image href='file:///...'> directive, the service resolves the local path. 4) The application reads the content of the target file into memory, performing re-encoding or inclusion processes. 5) The attacker observes the response-time latency differences to determine file existence or, in the case of image-based files, receives the disclosed content after the proxy re-encodes the data and presents the resulting stream.\nThe secondary impact is a sophisticated Denial of Service (DoS) vector. Because the service does not enforce limits on the number of requested assets or the total I/O volume, an attacker can embed multiple references to large local files or recursively reference files. This leads to unrestricted, high-volume I/O operations that saturate the system's storage bus and exhaust memory resources. Proof-of-concept demonstrations have verified that a single malicious request can trigger over 4.34 GB of I/O reads, effectively collapsing service availability.\nThe vulnerable component is the SVG processing pipeline used within the media proxy functionality of Stoatchat versions prior to 0.15.5. The lack of an 'allowlist' for URI schemes or a sandbox environment for rendering untrusted XML content facilitates these exploitation methods."
}