CVE-2026-73638 in Imager
Summary
by MITRE • 09/18/2026
Imager versions from 0.45_02 before 1.035 for Perl read outside the EXIF block via unchecked start offsets in tiff_load_ifd.
tiff_load_ifd() validates an IFD entry's data by checking that `entry->offset + entry->size` stays within the EXIF block, and never checks the start offset itself. Where that sum is not the real end of the data, the check passes with the entry starting outside the block.
Through 1.032 `entry->offset` is a plain int, so on the usual two's-complement implementations an offset with the high bit set converts to negative and the sum can land back inside the block. From 1.033 the field is a size_t and the addition wraps only where size_t is 32 bits. The IFD's own start offset is checked the same way and wraps where unsigned long is 32 bits, which includes 64-bit Windows.
Any caller of Imager->read() on an attacker-supplied image may receive EXIF tags holding bytes from outside the block, or crash the process.
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Analysis
by VulDB Data Team • 09/18/2026
The vulnerability in Perl's Imager module, specifically affecting versions prior to 1.035, represents a critical integer overflow and bounds checking failure within the TIFF Image File Directory loading routine. The core technical flaw resides in the tiff_load_ifd function, which is responsible for parsing EXIF metadata from image files. While the implementation attempts to validate that an IFD entry's data does not exceed the boundaries of the allocated EXIF block by verifying that the sum of the offset and size remains within limits, it fundamentally neglects to verify whether the starting offset itself falls outside the valid memory region. This omission creates a scenario where entries with invalid start positions can bypass validation checks if their calculated end position coincidentally lands back inside the allowed range due to integer arithmetic behavior.
The mechanics of this exploitation rely heavily on how signed and unsigned integers handle overflow in two's-complement systems. In versions up through 1.032, the entry offset is stored as a plain signed integer. When an attacker supplies a malicious image with a high-bit-set offset value, it converts to a negative number during processing. Adding a positive size to this negative offset can result in a sum that falls within the valid memory block, thereby passing the flawed boundary check despite the data actually residing outside the intended EXIF structure. This allows the parser to read arbitrary bytes from adjacent memory regions rather than restricting access strictly to the declared metadata area.
In versions 1.033 and later, the field type was changed to size_t, an unsigned integer type. While this mitigates some signed-integer issues, it introduces a different class of vulnerability related to arithmetic wrapping on specific architectures. On systems where size_t is thirty-two bits wide, or when dealing with IFD start offsets that utilize unsigned long types such as in sixty-four-bit Windows environments, the addition operation can wrap around due to overflow. This wrapping behavior similarly allows maliciously crafted inputs to satisfy boundary checks while actually accessing memory locations outside the designated EXIF block boundaries. The inconsistency between how different offset fields are validated further exacerbates the risk across various platform architectures.
The operational impact of this vulnerability is severe, encompassing both information disclosure and potential denial of service conditions. An attacker who can induce a victim to process a specially crafted image file using Imager's read function may cause the application to expose sensitive data from outside the EXIF block. This could lead to the leakage of internal memory contents, potentially revealing cryptographic keys, session tokens, or other confidential information stored in adjacent heap structures. Furthermore, if the out-of-bounds access targets unmapped or protected memory regions, it can trigger segmentation faults or similar crashes, resulting in a denial of service for applications relying on this library for image processing tasks.
This vulnerability aligns with CWE-125, Out-of-Bounds Read, as it involves reading data beyond the intended buffer boundary due to insufficient validation of input parameters. Additionally, from an offensive security perspective such as MITRE ATT&CK, this flaw facilitates Data Stealing via Local File or Remote Service Access if exploited in a web context where user-uploaded images are processed server-side. It also relates to CWE-190, Integer Overflow or Wraparound, which describes the arithmetic error that enables the bypass of security checks.
To mitigate these risks, organizations utilizing Perl's Imager module must upgrade immediately to version 1.035 or any subsequent release where this logic has been corrected. The fix involves implementing rigorous validation for both the start offset and the end boundary of EXIF entries, ensuring that neither value can be manipulated through integer overflow techniques. Developers should also consider adopting static analysis tools capable of detecting unsigned integer wraparounds and enforcing strict bounds checking on all memory access operations derived from untrusted image inputs. Regular security audits of third-party libraries are essential to maintain resilience against such low-level parsing vulnerabilities in widely used software components.