Bug 2459970 (CVE-2026-11850)

Summary: CVE-2026-11850 krb5: krb5: integer underflow in berval2tl_data() leads to heap out-of-bounds read
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: abokovoy, dschmidt, dymurray, eglynn, erezende, ibolton, jjoyce, jlanda, jmatthew, jmontleo, jpretori, jrische, jschluet, kshier, lhh, ljawale, luizcosta, mburns, mgarciac, nweather, pgaikwad, rbobbitt, rhel-process-autobot, rjohnson, simaishi, slucidi, smcdonal, sseago, stcannon, teagle, watson-tool-maintainers, yguenane
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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An integer underflow vulnerability was found in MIT krb5 in the berval2tl_data() function in plugins/kdb/ldap/libkdb_ldap/ldap_principal2.c. The function performs an unsigned subtraction (bv_len - 2) without a prior bounds check. When bv_len is 0 or 1, the subtraction wraps to a large value which is then truncated to uint16_t, yielding 0xFFFE (65534) or 0xFFFF (65535). The subsequent malloc succeeds and memcpy reads up to 65534 bytes from a 0-1 byte buffer, resulting in a heap out-of-bounds read. The attack vector involves a malicious or compromised LDAP KDB backend returning a krbExtraData attribute with bv_len < 2, triggering the underflow when the KDC or kadmind reads principal data.
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Description OSIDB Bzimport 2026-04-21 04:00:00 UTC 
An integer underflow vulnerability was found in MIT krb5 in the berval2tl_data() function in plugins/kdb/ldap/libkdb_ldap/ldap_principal2.c. The function performs an unsigned subtraction (bv_len - 2) without a prior bounds check. When bv_len is 0 or 1, the subtraction wraps to a large value which is then truncated to uint16_t, yielding 0xFFFE (65534) or 0xFFFF (65535). The subsequent malloc succeeds and memcpy reads up to 65534 bytes from a 0-1 byte buffer, resulting in a heap out-of-bounds read.

The attack vector involves a malicious or compromised LDAP KDB backend returning a krbExtraData attribute with bv_len < 2, triggering the underflow when the KDC or kadmind reads principal data.

Upstream fix: https://github.com/krb5/krb5/commit/2a5fd83
MIT ticket: https://krbdev.mit.edu/rt/Ticket/Display.html?id=9206