Predator and CL could not provide any possible suspects.
Using Code Search for the file, "BC_OnedEAN13Writer.cpp" assigning to the concern owner.

Suspecting Commit#
https://pdfium.googlesource.com/pdfium.git/+/e778668fe92b8c60e0537ee48f79d5af6c1a2f1e

@dsinclair -- Could you please look into the issue, kindly re-assign if this is not related to your changes.
Thank You.

hnakashima@ can you please take a look?

This is real bug, breaks barcode checksum.

Caused by https://pdfium-review.googlesource.com/c/pdfium/+/12210, fix incoming.

The following revision refers to this bug:
  https://pdfium.googlesource.com/pdfium/+/54b8137361f601148d266d779403ec0393113f39

commit 54b8137361f601148d266d779403ec0393113f39
Author: Henrique Nakashima <hnakashima@chromium.org>
Date: Thu Aug 31 16:21:48 2017

Fixing CBC_OnedEAN13Writer checksum.

Reverts a piece of
https://pdfium-review.googlesource.com/c/pdfium/+/12210

Bug:  chromium:760857 
Change-Id: I290ebb7b60a6508fc3e8fba6780c837d395c1c3b
Reviewed-on: https://pdfium-review.googlesource.com/12690
Reviewed-by: dsinclair <dsinclair@chromium.org>
Commit-Queue: Henrique Nakashima <hnakashima@chromium.org>

[modify] https://crrev.com/54b8137361f601148d266d779403ec0393113f39/fxbarcode/oned/BC_OnedEAN13Writer.cpp

ClusterFuzz has detected this issue as fixed in range 498952:499042.

Detailed report: https://clusterfuzz.com/testcase?key=4943959410606080

Fuzzer: libFuzzer_pdf_cfx_barcode_fuzzer
Job Type: libfuzzer_chrome_ubsan
Platform Id: linux

Crash Type: Integer-overflow
Crash Address: 
Crash State:
  CBC_OnedEAN13Writer::CalcChecksum
  CBC_EAN13::Preprocess
  CBC_EAN13::Encode
  
Sanitizer: undefined (UBSAN)

Regressed: https://clusterfuzz.com/revisions?job=libfuzzer_chrome_ubsan&range=498575:498629
Fixed: https://clusterfuzz.com/revisions?job=libfuzzer_chrome_ubsan&range=498952:499042

Reproducer Testcase: https://clusterfuzz.com/download?testcase_id=4943959410606080

See https://chromium.googlesource.com/chromium/src/+/master/testing/libfuzzer/reproducing.md for more information.

If you suspect that the result above is incorrect, try re-doing that job on the test case report page.

ClusterFuzz testcase 4943959410606080 is verified as fixed, so closing issue as verified.

If this is incorrect, please add ClusterFuzz-Wrong label and re-open the issue.