CVE-2026-93018 in Imager
Summary
by MITRE • 09/18/2026
Imager versions before 1.036 for Perl disclose uninitialised heap memory reading a paletted image with pixel indexes past its colour map in i_gpix_p and i_glin_p.
The palette is allocated uninitialised, and only the entries a reader adds count as populated. The TGA reader stores pixel indexes without checking them against the colour map. i_gpix_p() rejects only an index greater than the count, so an index equal to it reads the first unpopulated entry, and getpixel() returns it.
i_glin_p() skips any index at or beyond the count without writing that pixel to the caller's buffer. The palette-to-RGB conversion reads each row through an uninitialised buffer, so those pixels of the converted image hold prior heap contents.
Reading an attacker-supplied image through Imager->read() and then fetching its pixels or converting it to RGB discloses process heap memory.
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Analysis
by VulDB Data Team • 09/18/2026
The vulnerability in Perl's Imager module before version 1.036 constitutes a critical information disclosure flaw rooted in improper initialization of heap-allocated data structures during the processing of paletted images. Specifically, when handling Targa Graphics (TGA) files that utilize palette-based indexing, the library allocates memory for the color map but fails to zero-initialize this buffer prior to populating it with valid entries from the image file. This lack of initialization means that any portion of the allocated heap space not explicitly overwritten by legitimate palette data retains whatever values were previously stored there by other processes or earlier operations within the same program execution context. The core technical failure lies in the boundary checking logic implemented within the internal functions i_gpix_p and i_glin_p, which are responsible for retrieving pixel data based on index values provided by the image file header rather than user input directly.
The TGA reader component stores pixel indexes from the image without performing strict validation against the bounds of the populated color map entries. While the function i_gpix_p does perform a check to reject indices strictly greater than the count of valid palette entries, it erroneously allows an index equal to that count. In zero-indexed arrays or buffers typical in C-based libraries like Imager, an index equal to the size represents the first element beyond the allocated and initialized range. Consequently, when such an out-of-bounds index is accessed, the system reads from the unpopulated portion of the heap buffer. Since this memory was not cleared, it contains residual data from prior allocations, effectively leaking sensitive information about the process's internal state to the caller through the getpixel interface.
A similar but distinct failure mode exists in the i_glin_p function, which is used for reading lines of pixels into a buffer. This routine skips writing any pixel whose index falls at or beyond the valid count limit, thereby preventing direct out-of-bounds reads via that specific path. However, it fails to account for the downstream consequences when these skipped indices are processed during palette-to-RGB conversion. The conversion process iterates through all pixels in the image row and attempts to map each index to an RGB value using the color map. For those pixels with invalid or out-of-bounds indexes that were not written to the output buffer by i_glin_p, the subsequent conversion logic still accesses the unpopulated entries of the palette array. Because this section of memory is uninitialized heap space, the resulting converted image contains raw heap contents rather than valid color data, thereby facilitating information leakage even when direct pixel retrieval via getpixel might be restricted or handled differently depending on the specific API call path taken by the application.
The operational impact of this vulnerability allows an attacker to disclose sensitive process heap memory simply by supplying a maliciously crafted TGA image file and invoking standard Imager methods such as read, followed by either fetching individual pixels or converting the entire image to RGB format. This constitutes a classic buffer over-read scenario where insufficient bounds checking leads to unauthorized access to protected memory regions. The leaked data can potentially reveal cryptographic keys, session tokens, passwords, or other sensitive information stored in adjacent heap allocations, depending on what was previously loaded into that memory segment. In web applications using Perl and Imager for image processing, this could lead to severe confidentiality breaches if the processed images are part of a request-response cycle where output is returned to the user.
From a classification perspective, this vulnerability aligns with CWE-125, Out-of-bounds Read, as it involves reading memory beyond the intended buffer boundary due to improper validation of array indices. It also relates to CWE-908, Use of Uninitialized Resource, because the color map buffer is allocated but not properly initialized before use, leading to non-deterministic behavior and data leakage. In terms of attack vectors, this falls under ATT&CK technique T1537, Transfer Data to Cloud Account or External System via Web Service, if the leaked heap data is exfiltrated through network requests triggered by the application logic processing these images. It also reflects aspects of CWE-209, Generation of Error Message Containing Sensitive Information, as the error handling or output generation mechanisms inadvertently expose internal memory states to external entities.
Mitigation strategies must focus on immediate patching and defensive coding practices. The primary remediation is to upgrade Imager to version 1.036 or later, where these boundary checks have been corrected to ensure that all palette indices are strictly validated against the actual number of populated entries in the color map. Developers should also implement strict input validation for any image processing libraries used within their applications, ensuring that file formats and internal structures conform to expected specifications before processing begins. Additionally, employing memory sanitization tools such as AddressSanitizer during development can help detect similar uninitialized read vulnerabilities early in the software lifecycle. For systems unable to upgrade immediately, implementing a sandboxed environment with restricted heap access or using alternative image libraries with more rigorous security models may provide temporary relief against exploitation of this specific flaw.