Bug 2538431 (CVE-2026-93599)

Summary:	CVE-2026-93599 rustls-webpki: rustls-webpki: Denial of Service via crafted Certificate Revocation List
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security DevOps Team <prodsec-dev>
Status:	NEW ---	QA Contact:
Severity:	high	Docs Contact:
Priority:	high
Version:	unspecified	CC:	akhatavk, anpicker, anthomas, aos-team-art-private, aprice, asdas, bbrownin, blitton, bparees, brasmith, cochase, dbosanac, doconnor, dpaolell, dranck, dschmidt, eborisov, ehelms, gbenhaim, ggainey, gotiwari, hasun, hoberger, jcantril, jdelft, jfula, jhorak, jlanda, jowilson, jpasqual, jreimann, jsamir, jupierce, juwatts, kshier, lball, lgarciaa, lpele, mbarnett, mbiarnes, mdellweg, mdessi, mhulan, mrizzi, mvyas, ngough, niyer, nmoumoul, nyancey, oezr, ometelka, osousa, pcattana, pcreech, ppalepu, ppostler, prdhamdh, ptisnovs, rchan, rekumar, rhel-process-autobot, rjohnson, rojacob, sarad, sghai, sidsharm, simaishi, smallamp, sprizend, stcannon, suppawar, syedriko, tmalecek, twaugh, veshanka, vlaad, vvoronko, watson-tool-maintainers, xdharmai, yguenane
Target Milestone:	---	Keywords:	Security
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Hardware:	All
OS:	Linux
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Doc Text:	A flaw was found in rustls-webpki. A remote attacker, by influencing an application to parse a specially crafted Certificate Revocation List (CRL) that contains an empty `onlySomeReasons` value in its `issuingDistributionPoint` extension, could trigger a panic. This vulnerability leads to a denial of service (DoS) in applications that explicitly enable CRL revocation checking.	Story Points:	---
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oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
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Description OSIDB Bzimport 2026-09-22 18:32:34 UTC

rustls-webpki through 0.103.12 (and 0.104.0-alpha releases before 0.104.0-alpha.7) contains a reachable panic in bit_string_flags() in src/der.rs. The input guard fails to reject a named-bit BIT STRING whose content is exactly [0x00] (zero padding bits and no data bytes), so raw_bits.len() - 1 underflows on the empty slice and the subsequent index operation panics (subtract-with-overflow in debug, index-out-of-bounds in release). The condition is reachable through the public API BorrowedCertRevocationList::from_der() when a CRL contains an issuingDistributionPoint extension with such an onlySomeReasons value. Exploitation requires an application that explicitly opts in to CRL revocation checking by passing RevocationOptions to verify_for_usage() and that parses CRL bytes obtained from a source the attacker can influence; the default rustls configuration, which does not use RevocationOptions, is unaffected. A crafted CRL causes a denial of service via the panic. Fixed in 0.103.13 and 0.104.0-alpha.7.